Should remain format,looks almost the same as original.
A couple of examples:
This page discusses how to use software called pdftohtml to convert in Ubuntu.
This page lists shareware (probably Windows) which converts PDF to various MS formats, including htm.
I even found a couple of videos (a Google video and one on www.break.com). I didn't look at them because I think they'll just describe how to use some software.
These are obviously unsatisfactory if you want to know how to do it yourself.
I think PDF started out as a compressed 'postscript' file, but these days would probably contain images (of scanned documents, for example).
If that's the case, don't bother looking for text, you can extract the images and create HTML pages to display the images. This should at least enable you to preserve the formatting.
At the very least, you could screen-capture the PDF pages to create the images. Crude, I know, but it would work whether the PDF was postscript or images.