diff --git a/packages/pdfjs-viewer/scripts/update-viewer.ts b/packages/pdfjs-viewer/scripts/update-viewer.ts
index b38af11ba5..91f720d9ac 100644
--- a/packages/pdfjs-viewer/scripts/update-viewer.ts
+++ b/packages/pdfjs-viewer/scripts/update-viewer.ts
@@ -1,5 +1,6 @@
 import { join } from "path";
 import packageJson from "../package.json" with { type: "json" };
+import fs from "fs/promises";
 import * as yauzl from "yauzl";
 import { createWriteStream } from "fs";
 const version = packageJson.devDependencies["pdfjs-dist"];
@@ -46,7 +47,19 @@ async function main() {
             });
             zip.readEntry();
         });
+        zip.on("end", async () => {
+            console.log("Finished extracting pdfjs-dist files.");
+            await patchViewerHTML();
+        });
     });
 };
 
+async function patchViewerHTML() {
+    const viewerPath = join(__dirname, "../viewer/viewer.html");
+    let content = await fs.readFile(viewerPath, "utf-8");
+    content = content.replace(`    <link rel="stylesheet" href="viewer.css" />`, `    <link rel="stylesheet" href="viewer.css" />\n    <link rel="stylesheet" href="custom.css" />`);
+    content = content.replace(`  <script src="viewer.mjs" type="module"></script>`, `  <script src="custom.mjs" type="module"></script>\n  <script src="viewer.mjs" type="module"></script>`);
+    await fs.writeFile(viewerPath, content, "utf-8");
+}
+
 main();
diff --git a/packages/pdfjs-viewer/viewer/viewer.html b/packages/pdfjs-viewer/viewer/viewer.html
index 6b64bb3350..51850ceeb0 100644
--- a/packages/pdfjs-viewer/viewer/viewer.html
+++ b/packages/pdfjs-viewer/viewer/viewer.html
@@ -32,7 +32,9 @@ See https://github.com/adobe-type-tools/cmap-resources
 <script src="../build/pdf.mjs" type="module"></script>
 
     <link rel="stylesheet" href="viewer.css" />
+    <link rel="stylesheet" href="custom.css" />
 
+  <script src="custom.mjs" type="module"></script>
   <script src="viewer.mjs" type="module"></script>
   </head>