An assigment i’ve had in one or my IT SEC classes was to recover the content of a password protected PDF file. For that i used a program called pdfcrack that is available both for linux and windows
http://pdfcrack.sourceforge.net/
By simply running the program you’ll see what options to use.
First lets run a benchmark to see how many passwords can be checked using this tool.
To bruteforce the PDF file simply run PDFcrack “yourfile.pdf”
It will start to check every password combination, if the password is short it will recover the password. However if the password is longer 8 charachters or more, then it will take far too long time. In that case you’ll have to use a dictionary and hope the dictionary list contains the password.
You can do this by using the -w (wordlist) and select the wordlist to use.
Another option too speed up the cracking time is if you know one of the passwords
The PDF has a User password and a Owner password, if you know the User password you can enter it by using the -p and it will speed up the cracking.
