Acrobat (full version) does OCR on "scanned" PDFs, making a PDF with the text "behind" the scanned image - hence it still looks exactly like the original doc, but you can search. Acrobat also has multi-file search so you can search a whole hierarchy.

I've got one of the fuji scansnap multi-page scanners that:

a) Come with the full version of Acrobat
b) Come with an OCR program that will scan, OCR, and save multipage (and duplex) documents with a single press on the scanner's scan button.
c) Really are very good value. They even do colour.

See http://empegbbs.com/ubbthreads/showflat.php?Cat=0&Board=offtopic&Number=249655

Hugo