PDF.js not working on IE9
Try to load compatibility.js before pdf.js. Something like this:
<script type="text/javascript" src="/js/compatibility.js"></script> <script type="text/javascript" src="/js/pdf_compr.js"></script>
Browser support in their FAQs - check this as since the question was asked IE9 could have be supported: https://github.com/mozilla/pdf.js/wiki/Frequently-Asked-Questions#what-browsers-are-supported
PDF.JS and IE9 doesn't play too well together and I wouldn't rely on it if you want to support IE 9. Some of the rendering features in PDF.JS are not well progressed enough to be useable in IE9
There are ways to get around this, you can use FlexPaper which can be used in combination with PDF.js and a HTML4 version for browsers without HTML5 support
http://flexpaper.devaldi.com/demo/
(note; I am affiliated with FlexPaper product)