PDF file to be displayed on the dialog modal via bootstrap

You can also embed the pdf inside the modal. Like this:

<embed src="sample.pdf" frameborder="0" width="100%" height="400px">

That worked for me

Sorry to disappoint you but one cannot just show the pdf inside a modal by default. It is not an intended behavior. Even using <iframe>, you cannot render the pdf inside the bootstrap modal. Also most of the hacks provided online does not support cross-browser. The more ideal way is to use plugins for the same and I will give you the links for few using which you can achieve what you want.

1) Checkout PDFObject JS,

<script src="https://github.com/pipwerks/PDFObject/blob/master/pdfobject.min.js"></script>

PDFObject embeds PDF files into HTML documents. Link.

2) Easy Modal Plugin for Bootstrap. Demo Snippet and Website

3) Using jQuery Dialog Modal Popup Window. Demo.

Hope it helped.