Recover lost password on a PDF document using linux commandline tools

Recovering a lost password from a PDF document using Linux command-line tools can be tricky, especially if the PDF is encrypted with a strong password. However, if you have permission to access the PDF and are simply trying to recover a forgotten password, there are a few tools you can use. Here’s a step-by-step guide on how to do this. ### Prerequisites Make sure you have the following tools installed on your Linux system: 1. **pdftk**: A versatile tool for manipulating PDF files. 2. **pdfcrack**: A tool for recovering PDF passwords using brute-force attacks or dictionary attacks. You can install them using your package manager, e.g., on Debian-based systems: ```bash sudo apt-get install pdftk pdfcrack ``` ### Method 1: Using `pdftk` (if the password is known) If you know the password but want to remove it, you can use `pdftk` to create a new PDF without a password. ```bash pdftk input.pdf input_pw YOURPASSWORD output output.pdf ``` Replace `YOURPASSWORD` with your actual password and `input.pdf` with the name of your encrypted PDF file. ### Method 2: Using `pdfcrack` (for lost passwords) If you have lost the password, you can try to recover it using `pdfcrack`. Here’s how to do it: 1. **Run pdfcrack**: Open a terminal and type: ```bash pdfcrack -f input.pdf ``` This will attempt to crack the password. By default, it uses a brute-force method and may take a significant amount of time depending on the complexity of the password. 2. **Using a wordlist**: If you have a potential list of passwords, you can use the `-w` option to specify a wordlist. Create a text file (e.g., `passwords.txt`) and put your possible passwords in it. Then run: ```bash pdfcrack -f input.pdf -w passwords.txt ``` ### Method 3: Using `qpdf` (for known passwords) If you know the password and want to remove security, `qpdf` can also work well. 1. **Install qpdf**: Install `qpdf` if it’s not already installed. ```bash sudo apt-get install qpdf ``` 2. **Decrypt the PDF**: Run the following command with the known password: ```bash qpdf --decrypt --password=YOURPASSWORD input.pdf output.pdf ``` ### Important Note on Ethics and Legality Always ensure that you have the right to access the PDF file and that attempting to recover the password does not violate any legal agreements or privacy laws. Unauthorized access to files can lead to legal consequences. ### Conclusion Recovering a lost password from a PDF can be time-consuming and doesn't guarantee success, especially with strong passwords. Make sure to use these tools responsibly.