Most browsers can support PDF directly of via their plug-ins. Think about it first.
If you really need to convert PDF in HTML, you should understand that there is no one-to-one correspondence between their structures, so you should devise some mapping which would suit your, for example, imitate PDF look as close as possible, which is pretty much realistic. You should understand that, by its nature, HTML is fluid while PDF is tightly bound to the page rendering, it's a kind of "software paper".
If you really want to develop things in this way, I would recommend a .NET port of iText; it's called iTextSharp. This is all Open Source stuff. Please see:
] (you can download it here).