I presume you have tried Calibre to convert your pdfs to epub. I know it's not great, but better than nothing, and it's free!
Personally I use Abbyy FineReader to OCR the text to a doc file. Which I then edit and save as htm before finally using Calibre to create an epub from that.
Unfortunately not a lightweight or free option.
You could also have a look at these:
http://www.somepdf.com/
http://labnol.blogspot.com/2005/12/c...f-to-html.html
For conversion to plain text, e- mail the PDF file to
pdf2txt@adobe.com
For conversion to HTML, e-mail the file to
pdf2html@adobe.com