You can embed an iframe in your php page pointing to Google Doc Viewer and specifying the PDF file you want to display. This is the code you should add to your page:
<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!