The problem is: even though PDFs are widely used on the Web, this format is not a part of any W3 standards. That said, not all systems and browsers will support showing PDF in the browser at all. (For example, I recently totally exterminated anything related to Acrobat from the systems I use on regular basis, because I think it is disgusting, and now feel much better and view PDFs much faster; I don't suffer from the fact that my alternative product doesn't support any browsers.)
That said, you may need to represent your PDF content in the form of HTML, with some reasonable degree of approximation. Alternatively, you can show PDF preview as image.
To work with PDF, you can use, in particular:
http://en.wikipedia.org/wiki/IText[
^],
http://itextpdf.com/[
^],
http://sourceforge.net/projects/itextsharp/[
^].
See also this question and answer:
http://stackoverflow.com/questions/2295555/how-to-convert-pdf-into-html-using-c-sharp[
^].
—SA