Brute forcing PDF dumb passwords in a few seconds...

dumb-pdf-password-crack.sh

#!/usr/bin/env bash

# sudo apt install qpdf first if needed
# adjust range accordingly in lines 9 and 10

INPUT="$1"

printf "Bruteforcing password with numeric 4 digit key:\n"
time for i in $(seq 1 9999); do
        pass="$(printf '%04d' $i)" 
        printf "Trying '%s': " "$pass"
        qpdf --decrypt --password="$pass" "$INPUT" "$INPUT.decrypted.pdf" && {
                printf "Success!\n"
                exit 0
        }
done