Technique used - Brute Force
Requires Python 3.* and pikepdf
pip install pikepdf
python crack.py PATH_TO_PDF_FILE [-m MIN_DIGITS] [-n MAX_DIGITS] [-r MATCHING_REGEX]
Example 1 - If the password is between 3 to 5 digits long
python crack.py /home/elliot/Desktop/file.pdf -m 3 -n 5
Example 2 - Same as above, but tests passwords containing the digits 1-3 only
python crack.py /home/elliot/Desktop/file.pdf -m 3 -n 5 -r ^[1-3]+$