Script to decrypt PDFs using qpdf. Will ask for password only if needed.

decrypt_pdf.sh

#!/bin/bash

set -e -o pipefail

usage() {
    cat <<HELP

USAGE: $0 PDF_FILE [OUTPUT_DIR|OUTPUT_FILE]

Decrypts given pdf file usingh qpdf by prompting for a password.

Examples:
- $0 /path/to/example.pdf
    Will create /path/to/example_decrypted.pdf

- $0 /path/to/example.pdf output.pdf
    Will create output.pdf

- $0 /path/to/example.pdf /output_dir/
    Will create /output_dir/example_decrypted.pdf

- $0 /path/to/example.pdf /output_dir/output.pdf
    Will create /output_dir/output.pdf

Password can be provided using the PDF_PASSWORD environment variable.
HELP

}

if [[ $# -eq 0 ]];then
    usage
    exit 0
fi
PATH=$PATH:/opt/homebrew/bin
PDF="`realpath \"$1\"`"
PDF_NAME="`basename "$PDF"`"
OUT_NAME="${PDF_NAME/.PDF/.pdf}"
OUT_NAME="${OUT_NAME/.pdf/_decrypted.pdf}"
PDF_DIR="$(cd "$(dirname "$1")" && pwd)"
OUT_DIR="$PDF_DIR"

if [[ -n "$2" ]];then
    if [[ -d "$2" ]];then
        OUT_DIR="$(cd "$2" && pwd)"
    elif [[ -d `dirname "$2"` ]];then
        OUT_NAME="$(basename "$2")"
        OUT_DIR="$(cd `dirname "$2"` && pwd)"
    else
        echo "Bad output \"$2\""
        exit 1
    fi
fi

echo "Decrypting '${PDF_DIR}/${PDF_NAME}' => '${OUT_DIR}/${OUT_NAME}'"

OPTIONS=""

if qpdf --requires-password "${PDF_DIR}/${PDF_NAME}";then
    if [[ -z $PDF_PASSWORD ]];then
        read -s -p "Password: " PASS
        echo
        PDF_PASSWORD=$PASS
    fi
    OPTIONS="--verbose --decrypt --password=$PDF_PASSWORD"
fi

# echo qpdf "${PDF_DIR}/${PDF_NAME}" $OPTIONS "${OUT_DIR}/${OUT_NAME}"
qpdf "${PDF_DIR}/${PDF_NAME}" $OPTIONS "${OUT_DIR}/${OUT_NAME}"