It usually requires a lot of additional work, but the PDF files could be run through an OCR program to convert images of text into real text. It's about as far from a perfect process as you can get, and sometimes takes a lot of reformatting to get it near original condition.
Rich
Yes, and a good deal of the time running a OCR program will give you an error in the text. I would hate for this to be a full time job. Is this a job you are willing to take on?
Andrew