HOW TO: Open Password Protected PDF Documents
There are sometimes genuine reasons to unlock or crack a password protected PDF file. You have 
the legal right to open the encrypted PDF document but forgot the password like in the case below. Say one of your former colleague created some critical sales reports in PDF format but he is not working with the company anymore.
-In his absence, you have no option but to crack the PDF password in order to open, read or print these PDF files. How to Open Password Protected PDF Documents at Digital Inspiration