How to protect a PDF with a password

▶ 1. Two passwords with two different purposes

The PDF format provides for two distinct passwords, and confusing them leads to protecting the document differently from what you intended.

• ✓ Open password (user) — without it the document does not open at all. It is the strongest protection: whoever does not know it sees nothing.
• ✓ Owner password — the document opens freely, but certain operations such as printing, copying or editing stay blocked. It defines permissions, it does not prevent reading.

The two can be combined: opening reserved to those who hold the password and, once inside, permissions still restricted.

◆ 2. Setting up protection

The operation takes a few steps and ends with the download of an already encrypted document.

1. Install the extension from the download page and open the file with Choose a PDF.
2. Open the Protection and privacy panel.
3. In the Password protection section set the open password and, if needed, the owner one.
4. Choose the encryption algorithm: AES-256 is the current standard and the recommended choice; RC4 exists only for compatibility with very old readers.
5. Click Protect / sanitize and download to get the protected document.

⚖ 3. Restricting allowed actions

Beyond blocking access you can decide what may be done with the document once it is open.

1. In the Allowed actions section tick the operations you want to authorise.
2. You can separately control printing, text copying, content editing and adding annotations.
3. Blocking copying is useful on price lists and teaching material; blocking editing on contracts and final documents.
4. Consider leaving annotations enabled if the document is meant to be commented on by others.

👁 4. Cleaning hidden data

Protecting access is of limited use if the document carries information you did not intend to share.

1. In the Privacy cleanup section remove the metadata, which holds author, software and history.
2. Delete comments and annotations if they contain internal remarks.
3. Remove embedded attachments and JavaScript.
4. Use flatten form fields to fix the values entered.
5. If you need to remove genuinely confidential data from the text, a password is not enough: see the guide on how to remove confidential text.

🔑 5. Choosing and sharing the password

AES-256 encryption protected by a trivial password offers equally trivial security.

• ✓ Prefer a long passphrase to a short word with symbols: length matters more than complexity.
• ✓ Do not reuse a password you use elsewhere.
• ✓ Do not send the password in the same email as the document: use a different channel, such as a message or a phone call.
• ✓ If you lose the open password the document cannot be recovered: keep it in a password manager.

⚠ 6. What protection cannot do

It is worth being clear about the boundaries, so you do not place more trust in a password than it can bear.

• ✓ It does not stop someone who knows the password from passing the document on to anyone.
• ✓ It does not stop anyone photographing the screen or retyping the content by hand.
• ✓ It does not remove confidential data present in the document: it only makes it harder to reach.
• ✓ It does not attest who drafted the document: that is the job of a digital signature.

? 7. Frequently asked questions

The questions that come up most often on this topic.