Recently got an quote from a vendor, but needed to submit an invoice. The vendor was okay with me altering the PDF so the invoice could get submitted in time; however, they couldn’t make the change  and neither could I. I have full blown Acrobat 10, but the I didn’t have the password.

I found a link to that had some steps to get around the security.

http://www.wikihow.com/Unlock-a-Secure-PDF-File

The technique that worked best for me was the following website.

http://www.pdfunlock.com/

I hope this helps someone else out there….