Support Internet Explorer 11

It is recommended to stop supporting Internet Explorer 11 because it will not be supported by Microsoft on June 15, 2022
In order to support Internet Explorer (IE) 11, add the following polyfills to the entry point of your React application (index.html):
<html>
<head>
<!-- Polyfills for IE 11 -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/es6-shim/0.35.3/es6-shim.min.js"></script>
<script src="https://polyfill.io/v3/polyfill.min.js?features=IntersectionObserver"></script>
</head>
<body>
<div id="root"></div>
</body>
</html>

For pdf.js v2.6.347

The default build of pdfjs-dist v2.6.347 doesn't support IE 11. So if you are using this version of pdfjs-dist, you have to follow more steps:
  1. Point pdfjs-dist to its ES5 build
Assume that you're using Webpack to bundle the application, then set pdfjs-dist in the alias key:
// webpack.config.js
const path = require('path');
module.exports = {
entry: '...',
output: {
...
},
module: {
...
},
resolve: {
extensions: ['.js', '.jsx', '.ts', '.tsx'],
alias: {
// Point to ES5 build
'pdfjs-dist': path.resolve('./node_modules/pdfjs-dist/es5/build/pdf.js'),
},
},
};
  1. Set the worker path:
import { Worker } from '@react-pdf-viewer/core';
<Worker workerUrl='https://unpkg.com/pdfjs-dist@2.6.347/es5/build/pdf.worker.js'>