Ubuntu Unleashed

Dont you hate when you run into a locked down pdf on the web? I search google all the time for title filetype:pdf and some are locked, this is the solution! PDFCrack is a GNU/Linux (other POSIX-compatible systems should work too) tool for recovering passwords and content from PDF-files. It is small, command line driven without external dependencies. The application is Open Source (GPL).
Features

* Supports the standard security handler (revision 2 and 3) on all known PDF-versions
* Supports cracking both owner and userpasswords
* Both wordlists and bruteforcing the password is supported
* Simple permutations (currently only trying first character as Upper Case)
* Save/Load a running job
* Simple benchmarking
* Optimised search for owner-password when user-password is known


Install pdfcrack in Ubuntu

sudo aptitude install pdfcrack

pdfcrack Syntax

pdfcrack -f filename [options]

pdfcrack Options

-b, - -bench - Perform benchmark and exit.
-c, - -charset=STRING - Use the characters in STRING as charset.
-m, - -maxpw=INTEGER - Stop when reaching INTEGER as password length.
-n, - -minpw=INTEGER - Skip trying passwords shorter than INTEGER.
-l, - -loadState=FILE - Continue from the state saved in FILENAME.
-o, - -owner - Work with the ownerpassword.
-p, –password=STRING - Uses STRING as userpassword to speed up breaking ownerpassword (implies -o).
-q, - -quiet - Run quietly.
-s, - -permutate - Try permutating the passwords (currently only supports switching
first character to uppercase).
-u, - -user - Work with the userpassword (default).
-v, - -version - Print version and exit.
-w, - -wordlist=FILE - Use FILE as source of passwords to try.

pdfcrack Example

pdfcrack mylocked.pdf

More information on this great utility can be found @ the authors site here
Lifehacker.com Has some alternative utilities and ideas for cracking pdf's here
UbuntuGeek has some information about this tool here