pdf_unlock.go

/*
 * Unlocks PDF files, tries to decrypt encrypted documents with the given password,
 * if that fails it tries an empty password as best effort.
 *
 * Run as: go run pdf_unlock.go input.pdf <password> output.pdf
 */

package main

import (
	"fmt"
	"os"

	"github.com/unidoc/unipdf/v3/common/license"
	"github.com/unidoc/unipdf/v3/model"
)

func init() {
	// Make sure to load your metered License API key prior to using the library.
	// If you need a key, you can sign up and create a free one at https://cloud.unidoc.io
	err := license.SetMeteredKey(os.Getenv(`UNIDOC_LICENSE_API_KEY`))
	if err != nil {
		panic(err)
	}
}

func main() {
	if len(os.Args) < 4 {
		fmt.Printf("Usage: go run pdf_unlock.go input.pdf <password> output.pdf\n")
		os.Exit(1)
	}

	inputPath := os.Args[1]
	password := os.Args[2]
	outputPath := os.Args[3]

	err := unlockPdf(inputPath, outputPath, password)
	if err != nil {
		fmt.Printf("Error: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Complete, see output file: %s\n", outputPath)
}

func unlockPdf(inputPath string, outputPath string, password string) error {
	f, err := os.Open(inputPath)
	if err != nil {
		return err
	}

	defer f.Close()

	pdfReader, err := model.NewPdfReader(f)
	if err != nil {
		return err
	}

	isEncrypted, err := pdfReader.IsEncrypted()
	if err != nil {
		return err
	}

	// Try decrypting both with given password and an empty one if that fails.
	if isEncrypted {
		auth, err := pdfReader.Decrypt([]byte(password))
		if err != nil {
			return err
		}
		if !auth {
			return fmt.Errorf("Wrong password")
		}
	}

	// Generate a PdfWriter instance from existing PdfReader.
	pdfWriter, err := pdfReader.ToWriter(nil)
	if err != nil {
		return err
	}

	// Write to file.
	err = pdfWriter.WriteToFile(outputPath)
	return err
}