This has been tried many times, but I have never seen a generally acceptable solution for converting a webpage to a PDF-file. It might be possible for very specific, narrowly defined and formatted webpages based upon a template where the variable data can be plugged both into an HTML and a PDF template.

The main problem is that the HTML format is geared towards very fluid and flexible rendering, all depending on the output device whereas PDF is a format for a page, where pagination, position of pictures, font size and type, ... are all most strictly defined.

If you do not care about an exact 1-to-1 rendering between the webpage and the PDF file and the HTML does not try to "fix" the lay-out but rather uses the tags as semantic and structural guides, then it might just be possible to write a parser that can translate HTML to another format (I was thinking of TeX or LaTeX) that can be rendered into a PDF-file.