How to use the Protect PDF (Add Password)
- Drop the PDF on the box or click to choose it.
- Type the password people will need to open it, twice.
- Optionally open Permissions to block printing, copying or editing.
- Click Encrypt & download. The tool checks the result opens with your password before you get it.
How PDF password protection works
A protected PDF is encrypted: every text, image and font stream is scrambled with a random 256-bit key, and that key is locked with your password. Without the password a reader can’t decrypt the content at all. This tool uses the AES-256 method from PDF 2.0 (also supported since Acrobat 9 / PDF 1.7 extension level 3), which is what Adobe Acrobat uses by default today.
Open password vs permissions password
| Open (user) password | Permissions (owner) password | |
|---|---|---|
| Needed to | Open and read the file | Change security settings in an editor |
| Protection | Strong — content is encrypted | Advisory — relies on the reader respecting the flags |
| Typical use | Contracts, payslips, medical and financial records | Stopping casual printing or copying |
Choosing a good password
Encryption is only as strong as the password. Offline attacks try billions of guesses, so use at least 12 characters or a passphrase of four random words, and send it through a different channel than the file (for example, email the PDF and text the password). The password generator can make one for you.
Compatibility
AES-256 PDFs open in Adobe Acrobat and Reader 9+, Chrome, Edge, Firefox, macOS Preview, iOS and Android readers, and most modern apps. Very old readers (from before 2008) can’t open them. Digital signatures are not preserved, because encryption rewrites the file.
Private by design
Most online PDF services upload your document to their servers. This tool processes the file entirely in your browser with open-source libraries (pdf-lib and PDF.js), so contracts, invoices, bank statements and IDs never leave your device. It works offline once the page has loaded, and there are no file-count limits, watermarks or sign-ups.
Tools that pair well with the Protect PDF (Add Password)
- Compress PDF — Shrink PDFs for email, upload forms and websites.
- Merge PDF — Combine several PDF files into one document.
- Add Watermark to PDF — Stamp text such as CONFIDENTIAL, DRAFT or COPY across every page, centred, diagonal or tiled — with a live preview before you download.
- Split PDF — Pull specific pages out of a PDF, or break it into single pages or equal chunks.