diff --git a/app/package.json b/app/package.json
index 555fa8afb..8066f2461 100644
--- a/app/package.json
+++ b/app/package.json
@@ -207,6 +207,7 @@
       "@jupyterlab/mathjax2-extension",
       "@jupyterlab/markedparser-extension",
       "@jupyterlab/notebook-extension",
+      "@jupyterlab/pdf-extension",
       "@jupyterlab/rendermime-extension",
       "@jupyterlab/running-extension",
       "@jupyterlab/shortcuts-extension",
diff --git a/packages/application/src/app.ts b/packages/application/src/app.ts
index 5f1acc1e6..b11430932 100644
--- a/packages/application/src/app.ts
+++ b/packages/application/src/app.ts
@@ -6,6 +6,8 @@ import {
   JupyterFrontEndPlugin
 } from '@jupyterlab/application';
 
+import { Base64ModelFactory } from '@jupyterlab/docregistry';
+
 import { createRendermimePlugins } from '@jupyterlab/application/lib/mimerenderers';
 
 import { LabStatus } from '@jupyterlab/application/lib/status';
@@ -29,6 +31,9 @@ export class NotebookApp extends JupyterFrontEnd<INotebookShell> {
    */
   constructor(options: NotebookApp.IOptions = { shell: new NotebookShell() }) {
     super({ ...options, shell: options.shell ?? new NotebookShell() });
+
+    // Add initial model factory.
+    this.docRegistry.addModelFactory(new Base64ModelFactory());
     if (options.mimeExtensions) {
       for (const plugin of createRendermimePlugins(options.mimeExtensions)) {
         this.registerPlugin(plugin);