Code for PDF Viewer in Bootstrap Modal (Please Download ViewerJS from repository)
<!DOCTYPE html>
<html dir="ltr" mozdisallowselectionprint>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
<meta name="google" content="notranslate">
<title>PDF.js viewer </title>
<link rel="icon" type="image/png" href="da-white.png" />
<!-- links -->
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.3/css/all.min.css">
<link rel="stylesheet" href="bootstrap.min.css">
<!-- ref: https://viewerjs.org/instructions/ -->
</head>
<body>
<h1>Hello Devistic </h1>
<a type="button" style="width: 10rem; background-color: gray; border-radius: 4px; text-decoration: none; padding: 1rem; color:white;" data-toggle="modal" data-target="#pdfModal">Show PDF </a>
<!-- Bootstrap Modal -->
<div class="modal fade" id="pdfModal" tabindex="-1" role="dialog" aria-labelledby="pdfModalLabel" aria-hidden="true">
<div class="modal-dialog modal-lg">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="pdfModalLabel">PDF Viewer </h5>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">× </span>
</button>
</div>
<div class="modal-body">
<iframe id="pdfIframe" width="100%" height="500"> </iframe>
</div>
</div>
</div>
</div>
<!-- scripts -->
<script src="jquery.slim.min.js"> </script>
<script src="bootstrap.bundle.min.js"> </script>
</body>
</html>