Guide

How to password-protect a PDF

Lock a PDF so it needs a password to open, and decide whether readers can print, copy, or edit it, with real AES-256 encryption. Or take a password back off a file you own. Here is how.

Real encryption, applied last

pdfblah encrypts with AES-256, the same standard Acrobat uses. A password is not a watermark or a flag a viewer can ignore: the file's contents are genuinely scrambled until the password is entered. If you stack it with other changes, the password step always runs last, so it wraps everything else.

Lock a PDF online

1. Open pdfblah.com and drop in your PDF.
2. Add a change → Password-protect. Type the password readers will need to open it.
3. Choose permissions. You can allow or block printing, copying text, and editing, independently of the open password.
4. Download. The file is now encrypted.

Remove a password

If you know the current password, you can strip the encryption to get a clean copy, from the command line:

pdfblah unlock locked.pdf open.pdf --password "the current password"

pdfblah will not open a PDF you do not have the password for. This is a tool for locking and unlocking your own files, not for breaking into others.

Three ways to do it

Same engine every way, so the result is identical. Pick whichever fits:

• Online at pdfblah.com — nothing to install, free while we're testing.
• On your machine, free and private (nothing is uploaded): pip install pdfblah, then pdfblah gui opens the same tool in your browser.
• Command line, for scripts and bulk jobs:

pip install pdfblah

# require a password to open, and block copying
pdfblah protect in.pdf locked.pdf --password "s3cret" --no-copy

# allow opening freely but block editing and printing
pdfblah protect in.pdf locked.pdf --owner "admin" --no-modify --no-print

# remove a known password
pdfblah unlock locked.pdf open.pdf --password "s3cret"

The app and CLI are open source (MIT). See the pdfblah project on GitHub.