I guess most people know how to do this because it is so simple, but I have not seen it mentioned in the forum so far, so here it is.
To remove protection from a protectedpdf file -
1. Use a pdf password cracker (search for pdf password cracker on google) to remove the underlying password protection
2. open the unprotected pdf file using a pdf editor program (eg foxit pdf editor)
3. place your mouse over the black overlay and press the delete button. hey presto you now have an unprotected pdf document with ALL the security removed.