I’ve come across an PDF which was sent to my email from an automated banking system. Unfortunately, the PDF file is encrypted and I’ve no way of knowing the password (or actually I’ve forgotten the password).
Fortunately, my Ubuntu box comes with application which allows me to crack the PDF file within a reasonable time.
Using ‘pdfcrack’ to crack PDF file
You need to install pdfcrack to crack pdf file. In Ubuntu/Debian system, you simply need to run
sudo apt-get -y install pdfcrack
Then for actual cracking, you can run
pdfcrack -n5 -m10 encrypted.pdf
Where -n [minimum length] to brute-force, and -m [maximum length] to brute-force.
pdfcrack can also accept a file input containing list of words (dictionary attack). For dictionary-attack just run
pdfcrack --wordlist=dictionary.txt encrypted.pdf