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

HELP

}

if [[ $# -eq 0 ]];then
    usage
    exit 0
fi

PDF_NAME=$(basename "$1")
OUT_NAME=${PDF_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
    read -s -p "Password: " PASS
    echo
    OPTIONS="--decrypt --password=$PASS"
fi

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