Remove ng2-pdf-viewer and use only native viewer

src-ui/package.json

@@ -24,7 +24,6 @@
     "@ng-select/ng-select": "^5.0.9",
     "bootstrap": "^4.5.0",
     "ng-bootstrap": "^1.6.3",
-    "ng2-pdf-viewer": "^6.3.2",
     "ngx-cookie-service": "^10.1.1",
     "ngx-file-drop": "^10.0.0",
     "ngx-infinite-scroll": "^9.1.0",