Simplify the serializer checks

See https://github.com/paperless-ngx/paperless-ngx/discussions/13467

docs/api.md

@@ -227,6 +227,7 @@ Version-aware endpoints:
 - `PATCH /api/documents/{id}/`: content updates target the selected version (`?version={version_id}`) or latest version by default; non-content metadata updates target the root document.
 - `GET /api/documents/{id}/download/`, `GET /api/documents/{id}/preview/`, `GET /api/documents/{id}/thumb/`, `GET /api/documents/{id}/metadata/`: accept `?version={version_id}`.
 - `POST /api/documents/{id}/update_version/`: uploads a new version using multipart form field `document` and optional `version_label`.
+- `POST /api/documents/merge_as_versions/`: merges existing top-level documents as versions of a selected root. The JSON body must contain `documents` (at least two document IDs) and `root_document_id` (one of those IDs). When merging one source document, an optional `version_label` may be provided.
 - `PATCH /api/documents/{id}/versions/{version_id}/`: updates the `version_label` of a specific version.
 - `DELETE /api/documents/{root_id}/versions/{version_id}/`: deletes a non-root version.
 

docs/usage.md

@@ -99,6 +99,10 @@ Think of versions as **file history** for a document.
 - By default, search and document content use the latest version.
 - In document detail, selecting a version switches the preview, file metadata and content (and download etc buttons) to that version.
 - Deleting a non-root version keeps metadata and falls back to the latest remaining version.
+- From the document list, select two or more documents and choose **Merge as versions** to combine them under one entry. Select the root document whose metadata and permissions should be retained; the other selected documents become file versions. The root may already have versions, but documents being added as versions must not have version histories of their own.
+- From a document's **Versions** menu, choose **Existing** to search for another document and add it as a version of the current document.
+- Documents merged as versions give up their archive serial number. If the root has no ASN of its own it takes the first one, otherwise the ASNs are released and the removal is logged.
+- Merging as versions cannot be undone from the UI, and deleting the root document moves its versions to the trash as well.
 
 ### Management Lists
 

src-ui/src/app/components/common/confirm-dialog/merge-as-versions-confirm-dialog/merge-as-versions-confirm-dialog.component.html

@@ -0,0 +1,58 @@
+<div class="modal-header">
+  <h4 class="modal-title" id="modal-basic-title">{{title}}</h4>
+  <button type="button" class="btn-close" aria-label="Close" (click)="cancel()"></button>
+</div>
+<div class="modal-body">
+  <p>{{message}}</p>
+  <div class="form-group">
+    <label class="form-label" for="rootDocumentID" i18n>Root document:</label>
+    <select id="rootDocumentID" class="form-select" [ngModel]="rootDocumentID()" (ngModelChange)="rootDocumentID.set($event)">
+      @for (document of documents(); track document.id) {
+        <option [ngValue]="document.id">{{document.title}}</option>
+      }
+    </select>
+  </div>
+  <div class="form-group mt-4">
+    <span class="form-label d-inline-block" i18n>Versions (oldest first):</span>
+    <ul class="list-group"
+        cdkDropList
+        [cdkDropListData]="versionDocumentIDs()"
+        (cdkDropListDropped)="onDrop($event)">
+      @for (documentID of versionDocumentIDs(); track documentID) {
+        @let document = getDocument(documentID);
+        @if (document) {
+          <li class="list-group-item d-flex align-items-center" cdkDrag>
+            <i-bs name="grip-vertical" class="me-2"></i-bs>
+            <div class="d-flex flex-column">
+              <div>
+                @if (document.correspondent) {
+                  <b>{{document.correspondent | correspondentName | async}}: </b>
+                }{{document.title}}
+              </div>
+              <small class="text-muted">
+                {{document.created | customDate:'mediumDate'}}
+                @if (document.page_count) {
+                  | {document.page_count, plural, =1 {One page} other {{{document.page_count}} pages}}
+                }
+              </small>
+            </div>
+            @if ($last) {
+              <span class="badge bg-primary ms-auto" i18n>Current version</span>
+            }
+          </li>
+        }
+      }
+    </ul>
+    @if (versionDocumentIDs().length > 1) {
+      <div class="form-text" i18n>Drag to reorder.</div>
+    }
+  </div>
+</div>
+<div class="modal-footer">
+  <button type="button" class="btn" [class]="cancelBtnClass" (click)="cancel()" [disabled]="!buttonsEnabled()">
+    <span class="d-inline-block" style="padding-bottom: 1px;">{{cancelBtnCaption}}</span>
+  </button>
+  <button type="button" class="btn" [class]="btnClass" (click)="confirm()" [disabled]="!confirmButtonEnabled || !buttonsEnabled()">
+    {{btnCaption}}
+  </button>
+</div>

src-ui/src/app/components/common/confirm-dialog/merge-as-versions-confirm-dialog/merge-as-versions-confirm-dialog.component.scss

@@ -0,0 +1,3 @@
+.list-group-item {
+    cursor: move;
+}

src-ui/src/app/components/common/confirm-dialog/merge-as-versions-confirm-dialog/merge-as-versions-confirm-dialog.component.spec.ts

@@ -0,0 +1,70 @@
+import { provideHttpClient, withInterceptorsFromDi } from '@angular/common/http'
+import { provideHttpClientTesting } from '@angular/common/http/testing'
+import { ComponentFixture, TestBed } from '@angular/core/testing'
+import { NgbActiveModal } from '@ng-bootstrap/ng-bootstrap'
+import { NgxBootstrapIconsModule, allIcons } from 'ngx-bootstrap-icons'
+import { of } from 'rxjs'
+import { DocumentService } from 'src/app/services/rest/document.service'
+import { MergeAsVersionsConfirmDialogComponent } from './merge-as-versions-confirm-dialog.component'
+
+describe('MergeAsVersionsConfirmDialogComponent', () => {
+  let component: MergeAsVersionsConfirmDialogComponent
+  let fixture: ComponentFixture<MergeAsVersionsConfirmDialogComponent>
+  let documentService: DocumentService
+
+  beforeEach(async () => {
+    await TestBed.configureTestingModule({
+      imports: [
+        NgxBootstrapIconsModule.pick(allIcons),
+        MergeAsVersionsConfirmDialogComponent,
+      ],
+      providers: [
+        NgbActiveModal,
+        provideHttpClient(withInterceptorsFromDi()),
+        provideHttpClientTesting(),
+      ],
+    }).compileComponents()
+
+    fixture = TestBed.createComponent(MergeAsVersionsConfirmDialogComponent)
+    documentService = TestBed.inject(DocumentService)
+    component = fixture.componentInstance
+    fixture.detectChanges()
+  })
+
+  it('should fetch selected documents', () => {
+    const documents = [
+      { id: 1, title: 'Document 1' },
+      { id: 2, title: 'Document 2' },
+    ]
+    jest.spyOn(documentService, 'getFew').mockReturnValue(
+      of({
+        all: [1, 2],
+        count: 2,
+        results: documents,
+      })
+    )
+    component.documentIDs.set([1, 2])
+
+    component.ngOnInit()
+
+    expect(component.documents()).toEqual(documents)
+    expect(documentService.getFew).toHaveBeenCalledWith([1, 2])
+  })
+
+  it('should exclude the root from the draggable documents', () => {
+    component.documentIDs.set([1, 2, 3])
+    component.rootDocumentID.set(2)
+
+    expect(component.versionDocumentIDs()).toEqual([1, 3])
+  })
+
+  it('should move draggable documents while keeping the root fixed', () => {
+    component.documentIDs.set([1, 2, 3])
+    component.rootDocumentID.set(1)
+
+    component.onDrop({ previousIndex: 1, currentIndex: 0 } as any)
+
+    expect(component.documentIDs()).toEqual([1, 3, 2])
+    expect(component.versionDocumentIDs()).toEqual([3, 2])
+  })
+})

src-ui/src/app/components/common/confirm-dialog/merge-as-versions-confirm-dialog/merge-as-versions-confirm-dialog.component.ts

@@ -0,0 +1,70 @@
+import {
+  CdkDragDrop,
+  DragDropModule,
+  moveItemInArray,
+} from '@angular/cdk/drag-drop'
+import { AsyncPipe } from '@angular/common'
+import { Component, OnInit, computed, inject, signal } from '@angular/core'
+import { FormsModule } from '@angular/forms'
+import { NgxBootstrapIconsModule } from 'ngx-bootstrap-icons'
+import { takeUntil } from 'rxjs'
+import { Document } from 'src/app/data/document'
+import { CorrespondentNamePipe } from 'src/app/pipes/correspondent-name.pipe'
+import { CustomDatePipe } from 'src/app/pipes/custom-date.pipe'
+import { DocumentService } from 'src/app/services/rest/document.service'
+import { ConfirmDialogComponent } from '../confirm-dialog.component'
+
+@Component({
+  selector: 'pngx-merge-as-versions-confirm-dialog',
+  templateUrl: './merge-as-versions-confirm-dialog.component.html',
+  styleUrl: './merge-as-versions-confirm-dialog.component.scss',
+  imports: [
+    AsyncPipe,
+    CorrespondentNamePipe,
+    CustomDatePipe,
+    DragDropModule,
+    FormsModule,
+    NgxBootstrapIconsModule,
+  ],
+})
+export class MergeAsVersionsConfirmDialogComponent
+  extends ConfirmDialogComponent
+  implements OnInit
+{
+  private readonly documentService = inject(DocumentService)
+
+  readonly documentIDs = signal<number[]>([])
+  readonly documents = signal<Document[]>([])
+  readonly rootDocumentID = signal(-1)
+  readonly versionDocumentIDs = computed(() =>
+    this.documentIDs().filter(
+      (documentID) => documentID !== this.rootDocumentID()
+    )
+  )
+
+  ngOnInit() {
+    this.documentService
+      .getFew(this.documentIDs())
+      .pipe(takeUntil(this.unsubscribeNotifier))
+      .subscribe((response) => this.documents.set(response.results))
+  }
+
+  onDrop(event: CdkDragDrop<number[]>) {
+    const versionDocumentIDs = this.versionDocumentIDs().concat()
+    moveItemInArray(versionDocumentIDs, event.previousIndex, event.currentIndex)
+
+    // The root keeps its place in the list, only the versions move around it
+    let versionIndex = 0
+    this.documentIDs.update((documentIDs) =>
+      documentIDs.map((documentID) =>
+        documentID === this.rootDocumentID()
+          ? documentID
+          : versionDocumentIDs[versionIndex++]
+      )
+    )
+  }
+
+  getDocument(documentID: number): Document | undefined {
+    return this.documents().find((document) => document.id === documentID)
+  }
+}

src-ui/src/app/components/common/confirm-dialog/merge-confirm-dialog/merge-confirm-dialog.component.html

@@ -36,7 +36,7 @@
         </div>
     <div class="form-group mt-4">
         <label class="form-label" for="metadataDocumentID" i18n>Use metadata from:</label>
-        <select class="form-select" [ngModel]="metadataDocumentID()" (ngModelChange)="metadataDocumentID.set($event)">
+        <select id="metadataDocumentID" class="form-select" [ngModel]="metadataDocumentID()" (ngModelChange)="metadataDocumentID.set($event)">
             <option [ngValue]="-1" i18n>Regenerate all metadata</option>
             @for (document of documents(); track document.id) {
               <option [ngValue]="document.id">{{document.title}}</option>

src-ui/src/app/components/document-detail/document-detail.component.spec.ts

@@ -467,13 +467,6 @@ describe('DocumentDetailComponent', () => {
     const docWithVersions = {
       ...doc,
       versions: [
-        {
-          id: doc.id,
-          added: new Date('2024-01-01T00:00:00Z'),
-          version_label: 'Original',
-          checksum: 'aaaa',
-          is_root: true,
-        },
         {
           id: 10,
           added: new Date('2024-01-02T00:00:00Z'),
@@ -481,6 +474,13 @@ describe('DocumentDetailComponent', () => {
           checksum: 'bbbb',
           is_root: false,
         },
+        {
+          id: doc.id,
+          added: new Date('2024-01-01T00:00:00Z'),
+          version_label: 'Original',
+          checksum: 'aaaa',
+          is_root: true,
+        },
       ],
     } as Document
 
@@ -1232,8 +1232,8 @@ describe('DocumentDetailComponent', () => {
 
     metadataSpy.mockClear()
     component.document().versions = [
-      { id: doc.id, is_root: true },
       { id: 10, is_root: false },
+      { id: doc.id, is_root: true },
     ] as any
     jest.spyOn(documentService, 'getPreviewUrl').mockReturnValue('preview-root')
     jest.spyOn(documentService, 'getThumbUrl').mockReturnValue('thumb-root')
@@ -1929,8 +1929,8 @@ describe('DocumentDetailComponent', () => {
     component.documentId.set(doc.id)
     component.document.set({ ...doc, versions: [] } as Document)
     const updatedVersions = [
-      { id: doc.id, is_root: true },
       { id: 10, is_root: false },
+      { id: doc.id, is_root: true },
     ] as any
     const openDoc = { ...doc, versions: [] } as Document
     jest.spyOn(openDocumentsService, 'getOpenDocument').mockReturnValue(openDoc)
@@ -2046,8 +2046,8 @@ describe('DocumentDetailComponent', () => {
   it('should include version in download and print only for non-latest selected version', () => {
     initNormally()
     component.document().versions = [
-      { id: doc.id, is_root: true },
       { id: 10, is_root: false },
+      { id: doc.id, is_root: true },
     ] as any
 
     const getDownloadUrlSpy = jest

src-ui/src/app/components/document-detail/document-detail.component.ts

@@ -889,13 +889,9 @@ export class DocumentDetailComponent
 
   updateComponent(doc: Document) {
     this.document.set(doc)
-    // Default selected version is the newest version
+    // Default selected version is the newest version, which the API returns first
     const versions = doc.versions ?? []
-    this.selectedVersionId.set(
-      versions.length
-        ? Math.max(...versions.map((version) => version.id))
-        : doc.id
-    )
+    this.selectedVersionId.set(versions.length ? versions[0].id : doc.id)
     this.previewLoaded.set(false)
     this.requiresPassword = false
     this.updateFormForCustomFields()
@@ -1441,7 +1437,8 @@ export class DocumentDetailComponent
     if (!versions.length || !this.selectedVersionId()) {
       return null
     }
-    const latestVersionId = Math.max(...versions.map((version) => version.id))
+    // The API returns versions newest first
+    const latestVersionId = versions[0].id
     return this.selectedVersionId() === latestVersionId
       ? null
       : this.selectedVersionId()

src-ui/src/app/components/document-detail/document-version-dropdown/add-existing-document-version-dialog/add-existing-document-version-dialog.component.html

@@ -0,0 +1,18 @@
+<div class="modal-header">
+  <h4 class="modal-title" i18n>Add existing document as version</h4>
+  <button type="button" class="btn-close" aria-label="Close" (click)="cancel()"></button>
+</div>
+<div class="modal-body">
+  <pngx-input-document-link
+    [(ngModel)]="selectedDocumentIDs"
+    [parentDocumentID]="rootDocumentID"
+    [minimal]="true"
+    placeholder="Search for a document"
+    i18n-placeholder
+  ></pngx-input-document-link>
+  <div class="form-text mt-2" i18n>Select one document to add as a version.</div>
+</div>
+<div class="modal-footer">
+  <button type="button" class="btn btn-outline-secondary" (click)="cancel()" [disabled]="!buttonsEnabled()" i18n>Cancel</button>
+  <button type="button" class="btn btn-primary" (click)="confirm()" [disabled]="!buttonsEnabled() || selectedDocumentIDs.length !== 1" i18n>Add version</button>
+</div>

src-ui/src/app/components/document-detail/document-version-dropdown/add-existing-document-version-dialog/add-existing-document-version-dialog.component.spec.ts

@@ -0,0 +1,73 @@
+import { ComponentFixture, TestBed } from '@angular/core/testing'
+import { NgbActiveModal } from '@ng-bootstrap/ng-bootstrap'
+import { DocumentService } from 'src/app/services/rest/document.service'
+import { AddExistingDocumentVersionDialogComponent } from './add-existing-document-version-dialog.component'
+
+describe('AddExistingDocumentVersionDialogComponent', () => {
+  let component: AddExistingDocumentVersionDialogComponent
+  let fixture: ComponentFixture<AddExistingDocumentVersionDialogComponent>
+  let activeModal: jest.Mocked<Pick<NgbActiveModal, 'dismiss'>>
+
+  beforeEach(async () => {
+    activeModal = { dismiss: jest.fn() }
+    await TestBed.configureTestingModule({
+      imports: [AddExistingDocumentVersionDialogComponent],
+      providers: [
+        {
+          provide: NgbActiveModal,
+          useValue: activeModal,
+        },
+        {
+          provide: DocumentService,
+          useValue: {},
+        },
+      ],
+    }).compileComponents()
+
+    fixture = TestBed.createComponent(AddExistingDocumentVersionDialogComponent)
+    component = fixture.componentInstance
+    component.rootDocumentID = 3
+    fixture.detectChanges()
+  })
+
+  it('should emit the single selected document', () => {
+    const emitSpy = jest.spyOn(component.confirmClicked, 'emit')
+    component.selectedDocumentIDs = [20]
+
+    component.confirm()
+
+    expect(emitSpy).toHaveBeenCalledWith(20)
+  })
+
+  it('should require exactly one selected document', () => {
+    const emitSpy = jest.spyOn(component.confirmClicked, 'emit')
+    component.selectedDocumentIDs = [20, 21]
+
+    component.confirm()
+
+    expect(emitSpy).not.toHaveBeenCalled()
+  })
+
+  it('should dismiss on cancel', () => {
+    component.cancel()
+
+    expect(activeModal.dismiss).toHaveBeenCalled()
+  })
+
+  it('should re-render the buttons when they are toggled from outside', async () => {
+    const cancelButton: HTMLButtonElement = fixture.nativeElement.querySelector(
+      '.modal-footer button'
+    )
+    expect(cancelButton.disabled).toBeFalsy()
+
+    // No detectChanges: the dropdown toggling this from a request callback is
+    // all that happens, and nothing else schedules a render for the modal
+    component.buttonsEnabled.set(false)
+    await fixture.whenStable()
+    expect(cancelButton.disabled).toBeTruthy()
+
+    component.buttonsEnabled.set(true)
+    await fixture.whenStable()
+    expect(cancelButton.disabled).toBeFalsy()
+  })
+})

src-ui/src/app/components/document-detail/document-version-dropdown/add-existing-document-version-dialog/add-existing-document-version-dialog.component.ts

@@ -0,0 +1,35 @@
+import {
+  Component,
+  EventEmitter,
+  Input,
+  Output,
+  inject,
+  signal,
+} from '@angular/core'
+import { FormsModule } from '@angular/forms'
+import { NgbActiveModal } from '@ng-bootstrap/ng-bootstrap'
+import { DocumentLinkComponent } from 'src/app/components/common/input/document-link/document-link.component'
+
+@Component({
+  selector: 'pngx-add-existing-document-version-dialog',
+  templateUrl: './add-existing-document-version-dialog.component.html',
+  imports: [DocumentLinkComponent, FormsModule],
+})
+export class AddExistingDocumentVersionDialogComponent {
+  private readonly activeModal = inject(NgbActiveModal)
+
+  @Input() rootDocumentID: number
+  @Output() confirmClicked = new EventEmitter<number>()
+
+  selectedDocumentIDs: number[] = []
+  readonly buttonsEnabled = signal(true)
+
+  confirm(): void {
+    if (this.selectedDocumentIDs.length !== 1) return
+    this.confirmClicked.emit(this.selectedDocumentIDs[0])
+  }
+
+  cancel(): void {
+    this.activeModal.dismiss()
+  }
+}

src-ui/src/app/components/document-detail/document-version-dropdown/document-version-dropdown.component.html

@@ -24,13 +24,26 @@
           class="visually-hidden"
           (change)="onVersionFileSelected($event)"
         />
-        <button
-          class="btn btn-sm btn-outline-secondary w-100"
-          (click)="versionFileInput.click()"
-          [disabled]="!userIsOwner || !userCanEdit"
-        >
-          <i-bs name="file-earmark-plus"></i-bs><span class="ps-1" i18n>Add new version</span>
-        </button>
+        <div class="btn-group btn-group-sm w-100">
+          <button
+            class="btn btn-sm btn-outline-secondary w-100"
+            (click)="versionFileInput.click()"
+            [disabled]="!userIsOwner || !userCanEdit"
+            title="Upload a new version"
+            i18n-title
+          >
+            <i-bs name="file-earmark-plus"></i-bs><span class="ps-1" i18n>Upload</span>
+          </button>
+          <button
+            class="btn btn-sm btn-outline-secondary w-100"
+            (click)="addExistingDocumentAsVersion()"
+            [disabled]="!userIsOwner || !userCanEdit"
+            title="Use an existing document"
+            i18n-title
+          >
+            <i-bs name="file-earmark"></i-bs><span class="ps-1" i18n>Existing</span>
+          </button>
+        </div>
       } @else {
         @switch (versionUploadState()) {
           @case (UploadState.Uploading) {

src-ui/src/app/components/document-detail/document-version-dropdown/document-version-dropdown.component.spec.ts

@@ -1,6 +1,7 @@
 import { DatePipe } from '@angular/common'
-import { SimpleChange } from '@angular/core'
+import { SimpleChange, signal } from '@angular/core'
 import { ComponentFixture, TestBed } from '@angular/core/testing'
+import { NgbModal } from '@ng-bootstrap/ng-bootstrap'
 import { NgxBootstrapIconsModule, allIcons } from 'ngx-bootstrap-icons'
 import { Subject, of, throwError } from 'rxjs'
 import { DocumentVersionInfo } from 'src/app/data/document'
@@ -19,12 +20,17 @@ describe('DocumentVersionDropdownComponent', () => {
   let documentService: jest.Mocked<
     Pick<
       DocumentService,
-      'deleteVersion' | 'getVersions' | 'uploadVersion' | 'updateVersionLabel'
+      | 'deleteVersion'
+      | 'getVersions'
+      | 'mergeDocumentsAsVersions'
+      | 'uploadVersion'
+      | 'updateVersionLabel'
     >
   >
   let toastService: jest.Mocked<Pick<ToastService, 'showError' | 'showInfo'>>
   let finished$: Subject<{ taskId: string }>
   let failed$: Subject<{ taskId: string; message?: string }>
+  let modalService: jest.Mocked<Pick<NgbModal, 'open'>>
 
   beforeEach(async () => {
     finished$ = new Subject<{ taskId: string }>()
@@ -32,9 +38,11 @@ describe('DocumentVersionDropdownComponent', () => {
     documentService = {
       deleteVersion: jest.fn(),
       getVersions: jest.fn(),
+      mergeDocumentsAsVersions: jest.fn(),
       uploadVersion: jest.fn(),
       updateVersionLabel: jest.fn(),
     }
+    modalService = { open: jest.fn() }
     toastService = {
       showError: jest.fn(),
       showInfo: jest.fn(),
@@ -61,6 +69,10 @@ describe('DocumentVersionDropdownComponent', () => {
           provide: ToastService,
           useValue: toastService,
         },
+        {
+          provide: NgbModal,
+          useValue: modalService,
+        },
         {
           provide: WebsocketStatusService,
           useValue: {
@@ -222,9 +234,10 @@ describe('DocumentVersionDropdownComponent', () => {
   })
 
   it('onVersionFileSelected should upload and update versions after websocket success', () => {
+    // Newest first, as the API returns them
     const versions: DocumentVersionInfo[] = [
-      { id: 3, is_root: true, checksum: 'aaaa' },
       { id: 20, is_root: false, checksum: 'cccc' },
+      { id: 3, is_root: true, checksum: 'aaaa' },
     ]
     const file = new File(['test'], 'new-version.pdf', {
       type: 'application/pdf',
@@ -323,4 +336,45 @@ describe('DocumentVersionDropdownComponent', () => {
     expect(component.editingVersionId).toBeNull()
     expect(component.versionLabelDraft).toEqual('')
   })
+
+  it('addExistingDocumentAsVersion should merge with a label and refresh versions', () => {
+    const confirmClicked = new Subject<number>()
+    const modal = {
+      componentInstance: {
+        rootDocumentID: null,
+        buttonsEnabled: signal(true),
+        confirmClicked,
+      },
+      close: jest.fn(),
+    }
+    modalService.open.mockReturnValue(modal as any)
+    documentService.mergeDocumentsAsVersions.mockReturnValue(of({} as any))
+    // Newest first, as the API returns them. The merged document has a lower id
+    // than the root, which is the whole point of merging an existing document.
+    const versions: DocumentVersionInfo[] = [
+      { id: 2, is_root: false, checksum: 'cccc' },
+      { id: 3, is_root: true, checksum: 'aaaa' },
+    ]
+    documentService.getVersions.mockReturnValue(of({ id: 3, versions } as any))
+    component.newVersionLabel = '  Imported  '
+    const versionsEmitSpy = jest.spyOn(component.versionsUpdated, 'emit')
+    const selectedEmitSpy = jest.spyOn(component.versionSelected, 'emit')
+
+    component.addExistingDocumentAsVersion()
+    expect(modal.componentInstance.rootDocumentID).toEqual(3)
+    confirmClicked.next(2)
+
+    expect(documentService.mergeDocumentsAsVersions).toHaveBeenCalledWith(
+      [3, 2],
+      3,
+      'Imported'
+    )
+    expect(documentService.updateVersionLabel).not.toHaveBeenCalled()
+    expect(documentService.getVersions).toHaveBeenCalledWith(3)
+    expect(versionsEmitSpy).toHaveBeenCalledWith(versions)
+    expect(selectedEmitSpy).toHaveBeenCalledWith(2)
+    expect(component.newVersionLabel).toEqual('')
+    expect(modal.close).toHaveBeenCalled()
+    expect(toastService.showInfo).toHaveBeenCalled()
+  })
 })

src-ui/src/app/components/document-detail/document-version-dropdown/document-version-dropdown.component.ts

@@ -11,7 +11,7 @@ import {
   SimpleChanges,
 } from '@angular/core'
 import { FormsModule } from '@angular/forms'
-import { NgbDropdownModule } from '@ng-bootstrap/ng-bootstrap'
+import { NgbDropdownModule, NgbModal } from '@ng-bootstrap/ng-bootstrap'
 import { NgxBootstrapIconsModule } from 'ngx-bootstrap-icons'
 import { merge, of, Subject } from 'rxjs'
 import {
@@ -33,6 +33,7 @@ import {
   WebsocketStatusService,
 } from 'src/app/services/websocket-status.service'
 import { ConfirmButtonComponent } from '../../common/confirm-button/confirm-button.component'
+import { AddExistingDocumentVersionDialogComponent } from './add-existing-document-version-dialog/add-existing-document-version-dialog.component'
 
 @Component({
   selector: 'pngx-document-version-dropdown',
@@ -69,6 +70,7 @@ export class DocumentVersionDropdownComponent implements OnChanges, OnDestroy {
   private readonly documentsService = inject(DocumentService)
   private readonly toastService = inject(ToastService)
   private readonly websocketStatusService = inject(WebsocketStatusService)
+  private readonly modalService = inject(NgbModal)
   private readonly destroy$ = new Subject<void>()
   private readonly documentChange$ = new Subject<void>()
 
@@ -256,11 +258,10 @@ export class DocumentVersionDropdownComponent implements OnChanges, OnDestroy {
       .subscribe({
         next: (doc) => {
           if (uploadDocumentId !== this.documentId) return
-          if (doc?.versions) {
+          if (doc?.versions?.length) {
             this.versionsUpdated.emit(doc.versions)
-            this.versionSelected.emit(
-              Math.max(...doc.versions.map((version) => version.id))
-            )
+            // The API returns versions newest first
+            this.versionSelected.emit(doc.versions[0].id)
             this.clearVersionUploadStatus()
           }
         },
@@ -278,6 +279,55 @@ export class DocumentVersionDropdownComponent implements OnChanges, OnDestroy {
       })
   }
 
+  addExistingDocumentAsVersion(): void {
+    const modal = this.modalService.open(
+      AddExistingDocumentVersionDialogComponent,
+      { backdrop: 'static' }
+    )
+    const dialog =
+      modal.componentInstance as AddExistingDocumentVersionDialogComponent
+    dialog.rootDocumentID = this.documentId
+    dialog.confirmClicked
+      .pipe(takeUntil(this.destroy$), takeUntil(this.documentChange$))
+      .subscribe((existingDocumentID) => {
+        dialog.buttonsEnabled.set(false)
+        const versionLabel = this.newVersionLabel?.trim()
+        this.documentsService
+          .mergeDocumentsAsVersions(
+            [this.documentId, existingDocumentID],
+            this.documentId,
+            versionLabel
+          )
+          .pipe(
+            switchMap(() => this.documentsService.getVersions(this.documentId)),
+            first(),
+            finalize(() => dialog.buttonsEnabled.set(true)),
+            takeUntil(this.destroy$),
+            takeUntil(this.documentChange$)
+          )
+          .subscribe({
+            next: (document) => {
+              if (document?.versions?.length) {
+                this.versionsUpdated.emit(document.versions)
+                // The API returns versions newest first
+                this.versionSelected.emit(document.versions[0].id)
+              }
+              this.newVersionLabel = ''
+              modal.close()
+              this.toastService.showInfo(
+                $localize`Existing document added as a version.`
+              )
+            },
+            error: (error) => {
+              this.toastService.showError(
+                $localize`Error adding existing document as a version`,
+                error
+              )
+            },
+          })
+      })
+  }
+
   clearVersionUploadStatus(): void {
     this.versionUploadState.set(UploadState.Idle)
     this.versionUploadError.set(null)

src-ui/src/app/components/document-list/bulk-editor/bulk-editor.component.html

@@ -95,6 +95,9 @@
           <button ngbDropdownItem (click)="mergeSelected()" [disabled]="!userCanAdd || list.allSelected || list.selectedCount < 2">
             <i-bs name="journals" class="me-1"></i-bs><ng-container i18n>Merge</ng-container>
           </button>
+          <button ngbDropdownItem (click)="mergeSelectedAsVersions()" [disabled]="!userOwnsAll || !userCanEditAll || !userCanDelete || list.allSelected || list.selectedCount < 2">
+            <i-bs name="journal-bookmark-fill" class="me-1"></i-bs><ng-container i18n>Merge as versions</ng-container>
+          </button>
         </div>
       </div>
     </div>

src-ui/src/app/components/document-list/bulk-editor/bulk-editor.component.spec.ts

@@ -1248,6 +1248,89 @@ describe('BulkEditorComponent', () => {
     expect(documentListViewService.selected.size).toEqual(0)
   })
 
+  it('should support merging documents as versions', () => {
+    let modal: NgbModalRef
+    modalService.activeInstances.subscribe((m) => (modal = m[0]))
+    jest.spyOn(permissionsService, 'currentUserCan').mockReturnValue(true)
+    jest
+      .spyOn(documentListViewService, 'documents', 'get')
+      .mockReturnValue([{ id: 3 }, { id: 4 }])
+    jest.spyOn(documentService, 'getFew').mockReturnValue(
+      of({
+        all: [3, 4],
+        count: 2,
+        results: [
+          { id: 3, title: 'Document 3' },
+          { id: 4, title: 'Document 4' },
+        ],
+      })
+    )
+    jest
+      .spyOn(documentListViewService, 'selected', 'get')
+      .mockReturnValue(new Set([3, 4]))
+    jest
+      .spyOn(permissionsService, 'currentUserHasObjectPermissions')
+      .mockReturnValue(true)
+    jest
+      .spyOn(permissionsService, 'currentUserOwnsObject')
+      .mockReturnValue(true)
+    const mergeAsVersionsSpy = jest
+      .spyOn(documentService, 'mergeDocumentsAsVersions')
+      .mockReturnValue(of(true))
+    const toastInfoSpy = jest.spyOn(toastService, 'showInfo')
+    fixture.detectChanges()
+
+    component.mergeSelectedAsVersions()
+    expect(modal).not.toBeUndefined()
+    modal.componentInstance.rootDocumentID.set(4)
+    modal.componentInstance.confirm()
+
+    expect(mergeAsVersionsSpy).toHaveBeenCalledWith([3, 4], 4)
+    httpTestingController.match(
+      `${environment.apiBaseUrl}documents/?page=1&page_size=50&ordering=-created&truncate_content=true&include_selection_data=true`
+    )
+    httpTestingController.match(
+      `${environment.apiBaseUrl}documents/?page=1&page_size=100000&fields=id`
+    )
+    expect(documentListViewService.selected.size).toEqual(0)
+    expect(toastInfoSpy).toHaveBeenCalledWith('Documents merged as versions.')
+  })
+
+  it('should not report success when merging documents as versions fails', () => {
+    let modal: NgbModalRef
+    modalService.activeInstances.subscribe((m) => (modal = m[0]))
+    jest.spyOn(permissionsService, 'currentUserCan').mockReturnValue(true)
+    jest
+      .spyOn(documentListViewService, 'documents', 'get')
+      .mockReturnValue([{ id: 3 }, { id: 4 }])
+    jest.spyOn(documentService, 'getFew').mockReturnValue(
+      of({
+        all: [3, 4],
+        count: 2,
+        results: [
+          { id: 3, title: 'Document 3' },
+          { id: 4, title: 'Document 4' },
+        ],
+      })
+    )
+    jest
+      .spyOn(documentListViewService, 'selected', 'get')
+      .mockReturnValue(new Set([3, 4]))
+    jest
+      .spyOn(documentService, 'mergeDocumentsAsVersions')
+      .mockReturnValue(throwError(() => new Error('failed')))
+    const toastInfoSpy = jest.spyOn(toastService, 'showInfo')
+    const toastErrorSpy = jest.spyOn(toastService, 'showError')
+    fixture.detectChanges()
+
+    component.mergeSelectedAsVersions()
+    modal.componentInstance.rootDocumentID.set(4)
+    modal.componentInstance.confirm()
+
+    expect(toastErrorSpy).toHaveBeenCalled()
+    expect(toastInfoSpy).not.toHaveBeenCalled()
+  })
+
   it('should support bulk download with archive, originals or both and file formatting', () => {
     jest.spyOn(permissionsService, 'currentUserCan').mockReturnValue(true)
     jest

src-ui/src/app/components/document-list/bulk-editor/bulk-editor.component.ts

@@ -50,6 +50,7 @@ import { SettingsService } from 'src/app/services/settings.service'
 import { ToastService } from 'src/app/services/toast.service'
 import { flattenTags } from 'src/app/utils/flatten-tags'
 import { queryParamsFromFilterRules } from 'src/app/utils/query-params'
+import { MergeAsVersionsConfirmDialogComponent } from '../../common/confirm-dialog/merge-as-versions-confirm-dialog/merge-as-versions-confirm-dialog.component'
 import { MergeConfirmDialogComponent } from '../../common/confirm-dialog/merge-confirm-dialog/merge-confirm-dialog.component'
 import { RotateConfirmDialogComponent } from '../../common/confirm-dialog/rotate-confirm-dialog/rotate-confirm-dialog.component'
 import { CorrespondentEditDialogComponent } from '../../common/edit-dialog/correspondent-edit-dialog/correspondent-edit-dialog.component'
@@ -171,6 +172,13 @@ export class BulkEditorComponent
     )
   }
 
+  get userCanDelete(): boolean {
+    return this.permissionService.currentUserCan(
+      PermissionAction.Delete,
+      PermissionType.Document
+    )
+  }
+
   ngOnInit() {
     if (
       this.permissionService.currentUserCan(
@@ -287,14 +295,17 @@ export class BulkEditorComponent
   private executeDocumentAction(
     modal: NgbModalRef,
     request: Observable<any>,
-    options: { deleteOriginals?: boolean } = {}
+    options: { clearSelection?: boolean; successMessage?: string } = {}
   ) {
     if (modal) {
       modal.componentInstance.buttonsEnabled.set(false)
     }
     request.pipe(first()).subscribe({
       next: () => {
-        this.handleOperationSuccess(modal, options.deleteOriginals ?? false)
+        this.handleOperationSuccess(modal, options.clearSelection ?? false)
+        if (options.successMessage) {
+          this.toastService.showInfo(options.successMessage)
+        }
       },
       error: (error) => this.handleOperationError(modal, error),
     })
@@ -985,7 +996,7 @@ export class BulkEditorComponent
         this.executeDocumentAction(
           modal,
           this.documentService.mergeDocuments(mergeDialog.documentIDs(), args),
-          { deleteOriginals: !!args.delete_originals }
+          { clearSelection: !!args.delete_originals }
         )
         this.toastService.showInfo(
           $localize`Merged document will be queued for consumption.`
@@ -993,6 +1004,35 @@ export class BulkEditorComponent
       })
   }
 
+  mergeSelectedAsVersions() {
+    let modal = this.modalService.open(MergeAsVersionsConfirmDialogComponent, {
+      backdrop: 'static',
+    })
+    const mergeDialog =
+      modal.componentInstance as MergeAsVersionsConfirmDialogComponent
+    const documentIDs = Array.from(this.list.selected)
+    mergeDialog.title = $localize`Merge as versions`
+    mergeDialog.message = $localize`The selected documents will become versions of the root document.`
+    mergeDialog.btnCaption = $localize`Proceed`
+    mergeDialog.documentIDs.set(documentIDs)
+    mergeDialog.rootDocumentID.set(documentIDs[0])
+    mergeDialog.confirmClicked
+      .pipe(takeUntil(this.unsubscribeNotifier))
+      .subscribe(() => {
+        this.executeDocumentAction(
+          modal,
+          this.documentService.mergeDocumentsAsVersions(
+            mergeDialog.documentIDs(),
+            mergeDialog.rootDocumentID()
+          ),
+          {
+            clearSelection: true,
+            successMessage: $localize`Documents merged as versions.`,
+          }
+        )
+      })
+  }
+
   public setCustomFieldValues(changedCustomFields: ChangedItems) {
     const modal = this.modalService.open(CustomFieldsBulkEditDialogComponent, {
       backdrop: 'static',

src-ui/src/app/services/rest/document.service.spec.ts

@@ -316,6 +316,34 @@ describe(`DocumentService`, () => {
     })
   })
 
+  it('should call appropriate api endpoint for merging documents as versions', () => {
+    const ids = [1, 2, 3]
+    subscription = service.mergeDocumentsAsVersions(ids, 2).subscribe()
+    const req = httpTestingController.expectOne(
+      `${environment.apiBaseUrl}${endpoint}/merge_as_versions/`
+    )
+    expect(req.request.method).toEqual('POST')
+    expect(req.request.body).toEqual({
+      documents: ids,
+      root_document_id: 2,
+    })
+  })
+
+  it('should include an optional label when merging one document as a version', () => {
+    const ids = [1, 2]
+    subscription = service
+      .mergeDocumentsAsVersions(ids, 2, 'Imported')
+      .subscribe()
+    const req = httpTestingController.expectOne(
+      `${environment.apiBaseUrl}${endpoint}/merge_as_versions/`
+    )
+    expect(req.request.body).toEqual({
+      documents: ids,
+      root_document_id: 2,
+      version_label: 'Imported',
+    })
+  })
+
   it('should call appropriate api endpoint for edit pdf', () => {
     const ids = [1]
     const args = { operations: [{ page: 1, rotate: 90, doc: 0 }] }

src-ui/src/app/services/rest/document.service.ts

@@ -374,6 +374,18 @@ export class DocumentService extends AbstractPaperlessService<Document> {
     })
   }
 
+  mergeDocumentsAsVersions(
+    ids: number[],
+    rootDocumentId: number,
+    versionLabel?: string
+  ) {
+    return this.http.post(this.getResourceUrl(null, 'merge_as_versions'), {
+      documents: ids,
+      root_document_id: rootDocumentId,
+      ...(versionLabel ? { version_label: versionLabel } : {}),
+    })
+  }
+
   editPdfDocuments(ids: number[], request: EditPdfDocumentsRequest) {
     return this.http.post(this.getResourceUrl(null, 'edit_pdf'), {
       documents: ids,

src-ui/src/main.ts

@@ -115,6 +115,7 @@ import {
   house,
   inbox,
   infoCircle,
+  journalBookmarkFill,
   journals,
   link,
   listNested,
@@ -361,6 +362,7 @@ const icons = {
   house,
   inbox,
   infoCircle,
+  journalBookmarkFill,
   journals,
   link,
   listNested,

src/documents/bulk_edit.py

@@ -12,6 +12,7 @@ from celery import group
 from celery import shared_task
 from django.conf import settings
 from django.db import transaction
+from django.db.models import Max
 from django.db.models import Q
 from django.utils import timezone
 
@@ -30,6 +31,7 @@ from documents.permissions import set_permissions_for_object
 from documents.plugins.helpers import DocumentsStatusManager
 from documents.tasks import bulk_update_documents
 from documents.tasks import consume_file
+from documents.tasks import remove_document_from_index
 from documents.tasks import update_document_content_maybe_archive_file
 from documents.versioning import get_latest_version_for_root
 from documents.versioning import get_root_document
@@ -39,6 +41,9 @@ if TYPE_CHECKING:
 
     from django.contrib.auth.models import User
 
+if settings.AUDIT_LOG_ENABLED:
+    from auditlog.models import LogEntry
+
 logger: logging.Logger = logging.getLogger("paperless.bulk_edit")
 
 SourceMode = Literal["latest_version", "explicit_selection"]
@@ -612,6 +617,113 @@ def merge(
     return "OK"
 
 
+def merge_as_versions(
+    doc_ids: list[int],
+    *,
+    root_document_id: int,
+    version_label: str | None = None,
+    user: User | None = None,
+) -> Literal["OK"]:
+    with transaction.atomic():
+        documents = list(
+            Document.objects.select_for_update()
+            .filter(id__in=doc_ids)
+            .defer("content"),
+        )
+        documents_by_id = {document.id: document for document in documents}
+
+        source_ids = [doc_id for doc_id in doc_ids if doc_id != root_document_id]
+        root_document = documents_by_id[root_document_id]
+        next_version_index = (
+            Document.global_objects.filter(
+                root_document_id=root_document_id,
+            ).aggregate(max_index=Max("version_index"))["max_index"]
+            or 0
+        )
+
+        # A version gives up its ASN
+        source_asns = [
+            documents_by_id[source_id].archive_serial_number
+            for source_id in source_ids
+            if documents_by_id[source_id].archive_serial_number is not None
+        ]
+
+        updated_fields = ["root_document", "version_index", "archive_serial_number"]
+        if version_label is not None:
+            updated_fields.append("version_label")
+
+        for source_id in source_ids:
+            next_version_index += 1
+            source_document = documents_by_id[source_id]
+            source_document.root_document_id = root_document.pk
+            source_document.version_index = next_version_index
+            source_document.archive_serial_number = None
+            if version_label is not None:
+                source_document.version_label = version_label
+
+        # bulk_update and not save() to avoid post_save now
+        Document.objects.bulk_update(
+            [documents_by_id[source_id] for source_id in source_ids],
+            updated_fields,
+        )
+
+        root_updates = {"modified": timezone.now()}
+        if source_asns and root_document.archive_serial_number is None:
+            # If a version had one, hand the ASN over, the same as merge() does
+            root_updates["archive_serial_number"] = source_asns.pop(0)
+            logger.info(
+                f"Document {root_document.id} took archive serial number "
+                f"{root_updates['archive_serial_number']} from a document merged into it",
+            )
+        if source_asns:
+            logger.warning(
+                f"Archive serial number(s) {source_asns} were removed by merging "
+                f"those documents as versions of document {root_document.id}",
+            )
+
+        Document.objects.filter(pk=root_document.pk).update(**root_updates)
+
+        if settings.AUDIT_LOG_ENABLED:
+            # update() doesn't fire auditlog signals, so manual
+            LogEntry.objects.log_create(
+                instance=root_document,
+                changes={"Merged As Versions": ["None", source_ids]},
+                action=LogEntry.Action.UPDATE,
+                actor=user,
+                additional_data={
+                    "reason": "Merged as versions",
+                    "version_ids": source_ids,
+                },
+            )
+
+    # One batch rather than a task each
+    from documents.search import SearchIndexLockError
+    from documents.search import get_backend
+
+    try:
+        with get_backend().batch_update() as batch:
+            for source_id in source_ids:
+                batch.remove(source_id)
+    except SearchIndexLockError:
+        logger.error(
+            f"Search index lock exhausted removing {source_ids}, "
+            f"scheduling deferred index removal",
+        )
+        for source_id in source_ids:
+            remove_document_from_index.apply_async(args=[source_id], countdown=60)
+
+    bulk_update_documents.apply_async(
+        kwargs={"document_ids": [root_document_id]},
+        headers={"trigger_source": PaperlessTask.TriggerSource.SYSTEM},
+    )
+
+    # And as far as the frontend is concerned, they're deleted
+    status_mgr = DocumentsStatusManager()
+    status_mgr.send_documents_deleted(source_ids)
+
+    return "OK"
+
+
 def split(
     doc_ids: list[int],
     pages: list[list[int]],

src/documents/models.py

@@ -372,6 +372,10 @@ class Document(SoftDeleteModel, ModelWithOwner):  # type: ignore[django-manager-
         For version documents, this is always the document's own content.
         If the queryset already annotated ``effective_content``, that value is used.
         """
+        # Here to avoid circular import
+        from documents.versioning import sort_versions_newest_first
+        from documents.versioning import versions_newest_first
+
         if hasattr(self, "effective_content"):
             return getattr(self, "effective_content")
 
@@ -388,12 +392,10 @@ class Document(SoftDeleteModel, ModelWithOwner):  # type: ignore[django-manager-
             # Empty list means prefetch ran and found no versions — use own content.
             if not prefetched_versions:
                 return self.content
-            latest_prefetched = max(prefetched_versions, key=lambda doc: doc.id)
-            return latest_prefetched.content
+            return sort_versions_newest_first(prefetched_versions)[0].content
 
         latest_version_content = (
-            Document.objects.filter(root_document=self)
-            .order_by("-id")
+            versions_newest_first(Document.objects.filter(root_document=self))
             .values_list("content", flat=True)
             .first()
         )

src/documents/serialisers.py

@@ -88,6 +88,7 @@ from documents.templating.utils import convert_format_str_to_template_format
 from documents.templating.workflows import validate_workflow_template
 from documents.validators import uri_validator
 from documents.validators import url_validator
+from documents.versioning import sort_versions_newest_first
 
 if TYPE_CHECKING:
     from collections.abc import Iterable
@@ -1116,9 +1117,13 @@ class DocumentSerializer(
                 "added",
                 "checksum",
                 "version_label",
+                "root_document_id",
+                "version_index",
             )
             versions = [*versions_qs, root_doc]
 
+        versions = sort_versions_newest_first(versions)
+
         def build_info(doc: Document) -> _DocumentVersionInfo:
             return {
                 "id": doc.id,
@@ -1128,9 +1133,7 @@ class DocumentSerializer(
                 "is_root": doc.id == root_doc.id,
             }
 
-        info = [build_info(doc) for doc in versions]
-        info.sort(key=lambda item: item["id"], reverse=True)
-        return info
+        return [build_info(doc) for doc in versions]
 
     def get_original_file_name(self, obj) -> str | None:
         return obj.original_filename
@@ -1677,6 +1680,52 @@ class MergeDocumentsSerializer(DocumentListSerializer, SourceModeValidationMixin
     from_webui = serializers.BooleanField(required=False, default=False)
 
 
+class MergeDocumentsAsVersionsSerializer(DocumentListSerializer):
+    root_document_id = serializers.IntegerField(required=True)
+    version_label = serializers.CharField(
+        required=False,
+        allow_blank=True,
+        allow_null=True,
+        max_length=64,
+    )
+
+    def validate_version_label(self, value):
+        if value is None:
+            return None
+        normalized = value.strip()
+        return normalized or None
+
+    def validate(self, attrs):
+        documents = attrs["documents"]
+        if len(documents) < 2:
+            raise serializers.ValidationError(
+                "At least two documents are required.",
+            )
+        if attrs.get("version_label") is not None and len(documents) != 2:
+            raise serializers.ValidationError(
+                "version_label can only be used when merging one source document.",
+            )
+        if attrs["root_document_id"] not in documents:
+            raise serializers.ValidationError(
+                "root_document_id must be one of the selected documents.",
+            )
+
+        selected_documents = Document.objects.filter(id__in=documents)
+        if selected_documents.filter(root_document__isnull=False).exists():
+            raise serializers.ValidationError(
+                "Only top-level documents can be merged as versions.",
+            )
+
+        source_document_ids = set(documents) - {attrs["root_document_id"]}
+        if Document.global_objects.filter(
+            root_document_id__in=source_document_ids,
+        ).exists():
+            raise serializers.ValidationError(
+                "Documents with existing versions cannot be merged into another document.",
+            )
+        return attrs
+
+
 class EditPdfDocumentsSerializer(DocumentListSerializer, SourceModeValidationMixin):
     operations = serializers.ListField(required=True)
     delete_original = serializers.BooleanField(required=False, default=False)

src/documents/tests/test_api_document_versions.py

@@ -827,6 +827,67 @@ class TestDocumentVersioningApi(DirectoriesMixin, APITestCase):
         self.assertEqual(resp.status_code, status.HTTP_200_OK)
         self.assertEqual(resp.data["content"], "v1-content")
 
+    def _make_root_with_out_of_order_versions(self) -> tuple[Document, ...]:
+        """
+        A root whose newest version has a *lower* id than an older one, which is
+        what merging an existing document in as a version produces.
+        """
+        root = Document.objects.create(
+            title="root",
+            checksum="root",
+            mime_type="application/pdf",
+            content="root-content",
+        )
+        newest = Document.objects.create(
+            title="newest",
+            checksum="newest",
+            mime_type="application/pdf",
+            content="newest-content",
+        )
+        older = Document.objects.create(
+            title="older",
+            checksum="older",
+            mime_type="application/pdf",
+            root_document=root,
+            version_index=1,
+            content="older-content",
+        )
+        # Assigned last, so `newest` has the lower id despite being the later version
+        newest.root_document = root
+        newest.version_index = 2
+        newest.save()
+        return root, newest, older
+
+    def test_retrieve_uses_version_index_not_id_for_latest(self) -> None:
+        root, _, _ = self._make_root_with_out_of_order_versions()
+
+        resp = self.client.get(f"/api/documents/{root.id}/")
+
+        self.assertEqual(resp.status_code, status.HTTP_200_OK)
+        self.assertEqual(resp.data["content"], "newest-content")
+
+    def test_list_uses_version_index_not_id_for_latest(self) -> None:
+        self._make_root_with_out_of_order_versions()
+
+        resp = self.client.get("/api/documents/?fields=id,content")
+
+        self.assertEqual(resp.status_code, status.HTTP_200_OK)
+        self.assertEqual(
+            [doc["content"] for doc in resp.data["results"]],
+            ["newest-content"],
+        )
+
+    def test_versions_are_listed_newest_first_with_root_last(self) -> None:
+        root, newest, older = self._make_root_with_out_of_order_versions()
+
+        resp = self.client.get(f"/api/documents/{root.id}/")
+
+        self.assertEqual(resp.status_code, status.HTTP_200_OK)
+        self.assertEqual(
+            [(version["id"], version["is_root"]) for version in resp.data["versions"]],
+            [(newest.id, False), (older.id, False), (root.id, True)],
+        )
+
 
 class TestVersionAwareFilters(TestCase):
     def test_title_content_filter_falls_back_to_content(self) -> None:

src/documents/tests/test_api_schema.py

@@ -48,6 +48,7 @@ class TestApiSchema(APITestCase):
         self.assertIn("/api/documents/reprocess/", paths)
         self.assertIn("/api/documents/rotate/", paths)
         self.assertIn("/api/documents/merge/", paths)
+        self.assertIn("/api/documents/merge_as_versions/", paths)
         self.assertIn("/api/documents/edit_pdf/", paths)
         self.assertIn("/api/documents/remove_password/", paths)
 

src/documents/tests/test_merge_documents_as_versions.py

@@ -0,0 +1,546 @@
+import json
+from unittest import mock
+
+from auditlog.models import LogEntry
+from django.contrib.auth.models import Permission
+from django.contrib.auth.models import User
+from django.contrib.contenttypes.models import ContentType
+from django.test import TestCase
+from rest_framework import status
+from rest_framework.test import APITestCase
+
+from documents.bulk_edit import merge_as_versions
+from documents.models import Document
+from documents.serialisers import MergeDocumentsAsVersionsSerializer
+
+
+class TestMergeDocumentsAsVersionsSerializer(TestCase):
+    def setUp(self) -> None:
+        self.doc1 = Document.objects.create(checksum="A", title="A")
+        self.doc2 = Document.objects.create(checksum="B", title="B")
+        self.doc3 = Document.objects.create(checksum="C", title="C")
+
+    def test_accepts_selected_root_document(self) -> None:
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc2.id, self.doc3.id],
+                "root_document_id": self.doc2.id,
+            },
+        )
+
+        self.assertTrue(serializer.is_valid(), serializer.errors)
+        self.assertEqual(
+            serializer.validated_data,
+            {
+                "documents": [self.doc1.id, self.doc2.id, self.doc3.id],
+                "root_document_id": self.doc2.id,
+            },
+        )
+
+    def test_requires_at_least_two_documents(self) -> None:
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id],
+                "root_document_id": self.doc1.id,
+            },
+        )
+
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(
+            serializer.errors["non_field_errors"][0],
+            "At least two documents are required.",
+        )
+
+    def test_accepts_version_label_for_one_source_document(self) -> None:
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc1.id,
+                "version_label": "  Imported  ",
+            },
+        )
+
+        self.assertTrue(serializer.is_valid(), serializer.errors)
+        self.assertEqual(serializer.validated_data["version_label"], "Imported")
+
+    def test_rejects_version_label_for_multiple_source_documents(self) -> None:
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc2.id, self.doc3.id],
+                "root_document_id": self.doc1.id,
+                "version_label": "Imported",
+            },
+        )
+
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(
+            serializer.errors["non_field_errors"][0],
+            "version_label can only be used when merging one source document.",
+        )
+
+    def test_requires_root_document_to_be_selected(self) -> None:
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc3.id,
+            },
+        )
+
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(
+            serializer.errors["non_field_errors"][0],
+            "root_document_id must be one of the selected documents.",
+        )
+
+    def test_rejects_duplicate_documents(self) -> None:
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc1.id],
+                "root_document_id": self.doc1.id,
+            },
+        )
+
+        self.assertFalse(serializer.is_valid())
+        self.assertIn("documents", serializer.errors)
+
+    def test_rejects_selected_version(self) -> None:
+        version = Document.objects.create(
+            checksum="D",
+            title="D",
+            root_document=self.doc1,
+            version_index=1,
+        )
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [version.id, self.doc2.id],
+                "root_document_id": self.doc2.id,
+            },
+        )
+
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(
+            serializer.errors["non_field_errors"][0],
+            "Only top-level documents can be merged as versions.",
+        )
+
+    def test_rejects_source_document_with_versions(self) -> None:
+        Document.objects.create(
+            checksum="D",
+            title="D",
+            root_document=self.doc1,
+            version_index=1,
+        )
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc2.id,
+            },
+        )
+
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(
+            serializer.errors["non_field_errors"][0],
+            "Documents with existing versions cannot be merged into another document.",
+        )
+
+    def test_rejects_source_document_with_trashed_versions(self) -> None:
+        version = Document.objects.create(
+            checksum="D",
+            title="D",
+            root_document=self.doc1,
+            version_index=1,
+        )
+        version.delete()  # trashed, but still points at doc1
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc2.id,
+            },
+        )
+
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(
+            serializer.errors["non_field_errors"][0],
+            "Documents with existing versions cannot be merged into another document.",
+        )
+
+    def test_allows_root_document_with_versions(self) -> None:
+        Document.objects.create(
+            checksum="D",
+            title="D",
+            root_document=self.doc1,
+            version_index=1,
+        )
+        serializer = MergeDocumentsAsVersionsSerializer(
+            data={
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc1.id,
+            },
+        )
+
+        self.assertTrue(serializer.is_valid(), serializer.errors)
+
+
+class TestMergeDocumentsAsVersions(TestCase):
+    @mock.patch("documents.bulk_edit.DocumentsStatusManager")
+    @mock.patch("documents.bulk_edit.bulk_update_documents.apply_async")
+    @mock.patch("documents.search.get_backend")
+    def test_merges_documents_in_selection_order(
+        self,
+        get_backend_mock,
+        bulk_update_mock,
+        status_manager_mock,
+    ) -> None:
+        root = Document.objects.create(checksum="A", title="Root")
+        existing_version = Document.objects.create(
+            checksum="B",
+            title="Existing version",
+            root_document=root,
+            version_index=3,
+        )
+        source1 = Document.objects.create(
+            checksum="C",
+            title="Source 1",
+            archive_serial_number=1,
+        )
+        source2 = Document.objects.create(
+            checksum="D",
+            title="Source 2",
+            archive_serial_number=2,
+        )
+        original_modified = root.modified
+
+        result = merge_as_versions(
+            [source2.id, root.id, source1.id],
+            root_document_id=root.id,
+        )
+
+        self.assertEqual(result, "OK")
+        source1.refresh_from_db()
+        source2.refresh_from_db()
+        root.refresh_from_db()
+        # source2 was selected first, so it becomes the older of the two versions
+        self.assertEqual(source2.root_document_id, root.id)
+        self.assertEqual(source2.version_index, 4)
+        self.assertEqual(source1.root_document_id, root.id)
+        self.assertEqual(source1.version_index, 5)
+        self.assertIsNone(source1.archive_serial_number)
+        self.assertIsNone(source2.archive_serial_number)
+        # The root had no ASN of its own, so it takes the first one
+        self.assertEqual(root.archive_serial_number, 2)
+        self.assertGreater(root.modified, original_modified)
+        self.assertEqual(existing_version.root_document_id, root.id)
+
+        batch = get_backend_mock.return_value.batch_update.return_value.__enter__.return_value
+        self.assertEqual(
+            [call.args[0] for call in batch.remove.call_args_list],
+            [source2.id, source1.id],
+        )
+        bulk_update_mock.assert_called_once_with(
+            kwargs={"document_ids": [root.id]},
+            headers={"trigger_source": "system"},
+        )
+        status_manager_mock.return_value.send_documents_deleted.assert_called_once_with(
+            [source2.id, source1.id],
+        )
+
+    @mock.patch("documents.bulk_edit.DocumentsStatusManager")
+    @mock.patch("documents.bulk_edit.bulk_update_documents.apply_async")
+    @mock.patch("documents.search.get_backend")
+    def test_root_keeps_its_own_archive_serial_number(self, *_mocks) -> None:
+        root = Document.objects.create(
+            checksum="A",
+            title="Root",
+            archive_serial_number=1,
+        )
+        source = Document.objects.create(
+            checksum="B",
+            title="Source",
+            archive_serial_number=2,
+        )
+
+        with self.assertLogs("paperless.bulk_edit", level="WARNING") as logs:
+            merge_as_versions([root.id, source.id], root_document_id=root.id)
+
+        root.refresh_from_db()
+        source.refresh_from_db()
+        self.assertEqual(root.archive_serial_number, 1)
+        self.assertIsNone(source.archive_serial_number)
+        # Dropping an ASN is not silent
+        self.assertIn("[2]", logs.output[0])
+
+    @mock.patch("documents.bulk_edit.DocumentsStatusManager")
+    @mock.patch("documents.bulk_edit.bulk_update_documents.apply_async")
+    @mock.patch("documents.search.get_backend")
+    def test_root_without_asn_takes_the_source_archive_serial_number(
+        self,
+        *_mocks,
+    ) -> None:
+        root = Document.objects.create(checksum="A", title="Root")
+        source = Document.objects.create(
+            checksum="B",
+            title="Source",
+            archive_serial_number=7,
+        )
+
+        merge_as_versions([root.id, source.id], root_document_id=root.id)
+
+        root.refresh_from_db()
+        source.refresh_from_db()
+        self.assertEqual(root.archive_serial_number, 7)
+        self.assertIsNone(source.archive_serial_number)
+
+    @mock.patch("documents.bulk_edit.DocumentsStatusManager")
+    @mock.patch("documents.bulk_edit.bulk_update_documents.apply_async")
+    @mock.patch("documents.search.get_backend")
+    def test_writes_audit_log_entry(self, *_mocks) -> None:
+        user = User.objects.create_user(username="merger")
+        root = Document.objects.create(checksum="A", title="Root")
+        source = Document.objects.create(checksum="B", title="Source")
+        LogEntry.objects.all().delete()
+
+        merge_as_versions([root.id, source.id], root_document_id=root.id, user=user)
+
+        entry = LogEntry.objects.filter(
+            content_type=ContentType.objects.get_for_model(Document),
+            object_id=root.id,
+        ).first()
+        self.assertIsNotNone(entry)
+        self.assertEqual(entry.actor, user)
+        self.assertEqual(entry.action, LogEntry.Action.UPDATE)
+        self.assertEqual(entry.changes, {"Merged As Versions": ["None", [source.id]]})
+        self.assertEqual(entry.additional_data["version_ids"], [source.id])
+
+    @mock.patch("documents.bulk_edit.DocumentsStatusManager")
+    @mock.patch("documents.bulk_edit.bulk_update_documents.apply_async")
+    @mock.patch("documents.search.get_backend")
+    def test_sets_version_label_for_one_source_document(
+        self,
+        _get_backend_mock,
+        _bulk_update_mock,
+        _status_manager_mock,
+    ) -> None:
+        root = Document.objects.create(checksum="A", title="Root")
+        source = Document.objects.create(checksum="B", title="Source")
+
+        merge_as_versions(
+            [root.id, source.id],
+            root_document_id=root.id,
+            version_label="Imported",
+        )
+
+        source.refresh_from_db()
+        self.assertEqual(source.version_label, "Imported")
+
+
+class TestMergeDocumentsAsVersionsAPI(APITestCase):
+    def setUp(self) -> None:
+        self.user = User.objects.create_user(username="user")
+        self.user.user_permissions.add(
+            Permission.objects.get(codename="change_document"),
+            Permission.objects.get(codename="view_document"),
+            Permission.objects.get(codename="delete_document"),
+        )
+        self.doc1 = Document.objects.create(
+            checksum="A",
+            title="A",
+            owner=self.user,
+        )
+        self.doc2 = Document.objects.create(
+            checksum="B",
+            title="B",
+            owner=self.user,
+        )
+        self.client.force_authenticate(user=self.user)
+
+    @mock.patch("documents.views.bulk_edit.merge_as_versions")
+    def test_merges_documents_as_versions(self, merge_mock) -> None:
+        merge_mock.return_value = "OK"
+        merge_mock.__name__ = "merge_as_versions"
+
+        response = self.client.post(
+            "/api/documents/merge_as_versions/",
+            json.dumps(
+                {
+                    "documents": [self.doc1.id, self.doc2.id],
+                    "root_document_id": self.doc2.id,
+                    "version_label": "Imported",
+                },
+            ),
+            content_type="application/json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertEqual(response.data, {"result": "OK"})
+        merge_mock.assert_called_once_with(
+            [self.doc1.id, self.doc2.id],
+            root_document_id=self.doc2.id,
+            version_label="Imported",
+            user=self.user,
+        )
+
+    @mock.patch("documents.views.bulk_edit.merge_as_versions")
+    def test_requires_change_permission(self, merge_mock) -> None:
+        merge_mock.__name__ = "merge_as_versions"
+        user = User.objects.create_user(username="no-change")
+        self.doc1.owner = user
+        self.doc1.save()
+        self.doc2.owner = user
+        self.doc2.save()
+        self.client.force_authenticate(user=user)
+
+        response = self.client.post(
+            "/api/documents/merge_as_versions/",
+            {
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc1.id,
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_403_FORBIDDEN)
+        merge_mock.assert_not_called()
+
+    @mock.patch("documents.views.bulk_edit.merge_as_versions")
+    def test_requires_delete_permission(self, merge_mock) -> None:
+        merge_mock.__name__ = "merge_as_versions"
+        # Owns them and may change them, but may not make them stop being documents
+        user = User.objects.create_user(username="no-delete")
+        user.user_permissions.add(
+            Permission.objects.get(codename="change_document"),
+            Permission.objects.get(codename="view_document"),
+        )
+        for doc in (self.doc1, self.doc2):
+            doc.owner = user
+            doc.save()
+        self.client.force_authenticate(user=user)
+
+        response = self.client.post(
+            "/api/documents/merge_as_versions/",
+            {
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc1.id,
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_403_FORBIDDEN)
+        merge_mock.assert_not_called()
+
+    @mock.patch("documents.views.bulk_edit.merge_as_versions")
+    def test_rejects_unselected_root(self, merge_mock) -> None:
+        doc3 = Document.objects.create(
+            checksum="C",
+            title="C",
+            owner=self.user,
+        )
+
+        response = self.client.post(
+            "/api/documents/merge_as_versions/",
+            {
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": doc3.id,
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        merge_mock.assert_not_called()
+
+    @mock.patch("documents.views.bulk_edit.merge_as_versions")
+    def test_rejects_source_document_with_versions(self, merge_mock) -> None:
+        Document.objects.create(
+            checksum="C",
+            title="C",
+            root_document=self.doc1,
+            version_index=1,
+            owner=self.user,
+        )
+
+        response = self.client.post(
+            "/api/documents/merge_as_versions/",
+            {
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc2.id,
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        merge_mock.assert_not_called()
+        self.doc1.refresh_from_db()
+        self.assertIsNone(self.doc1.root_document_id)
+
+    @mock.patch("documents.bulk_edit.DocumentsStatusManager")
+    @mock.patch("documents.bulk_edit.bulk_update_documents.apply_async")
+    @mock.patch("documents.search.get_backend")
+    def test_merges_and_returns_documents_as_versions(
+        self,
+        get_backend_mock,
+        bulk_update_mock,
+        status_manager_mock,
+    ) -> None:
+        response = self.client.post(
+            "/api/documents/merge_as_versions/",
+            {
+                "documents": [self.doc1.id, self.doc2.id],
+                "root_document_id": self.doc2.id,
+                "version_label": "Imported",
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.doc1.refresh_from_db()
+        self.assertEqual(self.doc1.root_document_id, self.doc2.id)
+        self.assertEqual(self.doc1.version_label, "Imported")
+
+        detail_response = self.client.get(
+            f"/api/documents/{self.doc2.id}/?fields=id,versions",
+        )
+        self.assertEqual(detail_response.status_code, status.HTTP_200_OK)
+        versions = detail_response.data["versions"]
+        self.assertEqual(
+            {version["id"] for version in versions},
+            {self.doc1.id, self.doc2.id},
+        )
+        self.assertEqual(
+            [version["id"] for version in versions if version["is_root"]],
+            [self.doc2.id],
+        )
+        batch = get_backend_mock.return_value.batch_update.return_value.__enter__.return_value
+        batch.remove.assert_called_once_with(self.doc1.id)
+        bulk_update_mock.assert_called_once_with(
+            kwargs={"document_ids": [self.doc2.id]},
+            headers={"trigger_source": "system"},
+        )
+        status_manager_mock.return_value.send_documents_deleted.assert_called_once_with(
+            [self.doc1.id],
+        )
+
+    @mock.patch("documents.bulk_edit.DocumentsStatusManager")
+    @mock.patch("documents.bulk_edit.bulk_update_documents.apply_async")
+    @mock.patch("documents.search.get_backend")
+    def test_chosen_order_survives_to_the_versions_list(self, *_mocks) -> None:
+        doc3 = Document.objects.create(checksum="C", title="C", owner=self.user)
+        # Deliberately not in id order, as dragging the dialog rows produces
+        ordered = [doc3.id, self.doc1.id]
+
+        response = self.client.post(
+            "/api/documents/merge_as_versions/",
+            {
+                "documents": [*ordered, self.doc2.id],
+                "root_document_id": self.doc2.id,
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        detail_response = self.client.get(
+            f"/api/documents/{self.doc2.id}/?fields=id,versions",
+        )
+        # Newest first, so the reverse of the order they were merged in
+        self.assertEqual(
+            [version["id"] for version in detail_response.data["versions"]],
+            [self.doc1.id, doc3.id, self.doc2.id],
+        )

src/documents/versioning.py

@@ -5,12 +5,34 @@ from enum import StrEnum
 from typing import TYPE_CHECKING
 from typing import Any
 
+from django.db.models import F
+from django.db.models import QuerySet
+
 from documents.models import Document
 
 if TYPE_CHECKING:
     from rest_framework.request import Request
 
 
+def versions_newest_first(documents: QuerySet[Document]) -> QuerySet[Document]:
+    """
+    Sorts versions so the newest one comes first using version_index and not on id,
+    because an existing document can be merged in as a version
+    """
+    return documents.order_by(F("version_index").desc(nulls_last=True), "-id")
+
+
+def sort_versions_newest_first(documents: list[Document]) -> list[Document]:
+    """
+    Same sorting as versions_newest_first()
+    """
+    return sorted(
+        documents,
+        key=lambda doc: (doc.version_index or 0, doc.id),
+        reverse=True,
+    )
+
+
 class VersionResolutionError(StrEnum):
     INVALID = "invalid"
     NOT_FOUND = "not_found"
@@ -51,7 +73,7 @@ def get_latest_version_for_root(
     include_deleted: bool = False,
 ) -> Document:
     manager = _document_manager(include_deleted=include_deleted)
-    latest = manager.filter(root_document=root_doc).order_by("-id").first()
+    latest = versions_newest_first(manager.filter(root_document=root_doc)).first()
     return latest or root_doc
 
 

src/documents/views.py

@@ -195,6 +195,7 @@ from documents.serialisers import DocumentVersionLabelSerializer
 from documents.serialisers import DocumentVersionSerializer
 from documents.serialisers import EditPdfDocumentsSerializer
 from documents.serialisers import EmailSerializer
+from documents.serialisers import MergeDocumentsAsVersionsSerializer
 from documents.serialisers import MergeDocumentsSerializer
 from documents.serialisers import NotesSerializer
 from documents.serialisers import PostDocumentSerializer
@@ -232,6 +233,7 @@ from documents.versioning import get_latest_version_for_root
 from documents.versioning import get_request_version_param
 from documents.versioning import get_root_document
 from documents.versioning import resolve_requested_version_for_root
+from documents.versioning import versions_newest_first
 from paperless import version
 from paperless.celery import app as celery_app
 from paperless.config import AIConfig
@@ -1075,9 +1077,9 @@ class DocumentViewSet(
 
     def get_queryset(self):
         latest_version_content = Subquery(
-            Document.objects.filter(root_document=OuterRef("pk"))
-            .order_by("-id")
-            .values("content")[:1],
+            versions_newest_first(
+                Document.objects.filter(root_document=OuterRef("pk")),
+            ).values("content")[:1],
         )
         # A correlated subquery avoids the LEFT JOIN + Count() this used to
         # be, which forced a GROUP BY aggregate over every matching document
@@ -1113,6 +1115,7 @@ class DocumentViewSet(
                         "checksum",
                         "version_label",
                         "root_document_id",
+                        "version_index",
                     ),
                 ),
                 "tags",
@@ -2133,11 +2136,9 @@ class DocumentViewSet(
                 },
             )
 
-        current = (
-            Document.objects.filter(Q(id=root_doc.id) | Q(root_document=root_doc))
-            .order_by("-id")
-            .first()
-        )
+        current = versions_newest_first(
+            Document.objects.filter(Q(id=root_doc.id) | Q(root_document=root_doc)),
+        ).first()
 
         document_updated.send(
             sender=self.__class__,
@@ -2765,8 +2766,12 @@ class DocumentOperationPermissionMixin(PassUserMixin, DocumentSelectionMixin):
         "delete_pages",
         "edit_pdf",
         "remove_password",
+        "merge_as_versions",
+    }
+    # merge_as_versions doesn't queue any consume tasks
+    METHOD_NAMES_REQUIRING_TRIGGER_SOURCE = METHOD_NAMES_REQUIRING_USER - {
+        "merge_as_versions",
     }
-    METHOD_NAMES_REQUIRING_TRIGGER_SOURCE = METHOD_NAMES_REQUIRING_USER
 
     def _has_document_permissions(
         self,
@@ -2807,6 +2812,7 @@ class DocumentOperationPermissionMixin(PassUserMixin, DocumentSelectionMixin):
                     bulk_edit.rotate,
                     bulk_edit.delete_pages,
                     bulk_edit.edit_pdf,
+                    bulk_edit.merge_as_versions,
                     bulk_edit.remove_password,
                 ]
             )
@@ -2837,6 +2843,9 @@ class DocumentOperationPermissionMixin(PassUserMixin, DocumentSelectionMixin):
             has_perms
             and (
                 method == bulk_edit.delete
+                # Sources stop being documents of their own, and removing one
+                # again afterwards needs delete_document
+                or method == bulk_edit.merge_as_versions
                 or (
                     method in [bulk_edit.merge, bulk_edit.split]
                     and parameters.get("delete_originals")
@@ -3093,6 +3102,33 @@ class MergeDocumentsView(DocumentOperationPermissionMixin):
         )
 
 
+@extend_schema_view(
+    post=extend_schema(
+        operation_id="documents_merge_as_versions",
+        description="Merge selected documents as versions of a chosen root document",
+        responses={
+            200: inline_serializer(
+                name="MergeDocumentsAsVersionsResult",
+                fields={
+                    "result": serializers.CharField(),
+                },
+            ),
+        },
+    ),
+)
+class MergeDocumentsAsVersionsView(DocumentOperationPermissionMixin):
+    serializer_class = MergeDocumentsAsVersionsSerializer
+
+    def post(self, request, *args, **kwargs):
+        serializer = self.get_serializer(data=request.data)
+        serializer.is_valid(raise_exception=True)
+        return self._execute_document_action(
+            method=bulk_edit.merge_as_versions,
+            validated_data=serializer.validated_data,
+            operation_label="document merge as versions",
+        )
+
+
 @extend_schema_view(
     post=extend_schema(
         operation_id="documents_delete",

src/paperless/urls.py

@@ -27,6 +27,7 @@ from documents.views import EditPdfDocumentsView
 from documents.views import GlobalSearchView
 from documents.views import IndexView
 from documents.views import LogViewSet
+from documents.views import MergeDocumentsAsVersionsView
 from documents.views import MergeDocumentsView
 from documents.views import PostDocumentView
 from documents.views import RemoteVersionView
@@ -172,6 +173,11 @@ urlpatterns = [
                                 MergeDocumentsView.as_view(),
                                 name="merge_documents",
                             ),
+                            re_path(
+                                "^merge_as_versions/",
+                                MergeDocumentsAsVersionsView.as_view(),
+                                name="merge_documents_as_versions",
+                            ),
                             re_path(
                                 "^edit_pdf/",
                                 EditPdfDocumentsView.as_view(),