Embed an iframe inside a div pointing to Google Doc Viewer and specifying the PDF file you want to display. This is the code you should add:
<iframe src="http://docs.google.com/gview?url=http://infolab.stanford.edu/pub/papers/google.pdf&embedded=true" style="width:600px; height:500px;" frameborder="0"></iframe>
Then you just need to set up your own document file to the "url" query string param and that's it! You can display not just PDF but any other file supported by the viewer like doc, xls, etc.