Protect PDF

Protect PDF adds a password to a PDF and lets you choose what the recipient may do with it. Encryption is applied with QPDF in your browser, so the document never leaves your device. The original file is not changed.

How to protect a PDF with a password

1. Drop your PDF onto the tool or click Choose file. The tool shows the filename, page count and size.
2. Type an open password and confirm it. The strength guide is a rough indication, not a guarantee.
3. Optionally type a different owner password. If you leave it blank, the open password is used for both.
4. Choose permissions for printing, copying and changes.
5. Click Protect PDF and wait while QPDF encrypts a new copy.
6. Download <name>-protected.pdf. Keep the original and your password somewhere safe.

Open password versus owner password

Two passwords can be set. The open password (also called the user password) is the one a reader asks for before it will display the PDF. Without it, the contents stay encrypted.

The owner password controls permission changes and security settings. It is optional. If you leave it blank, the tool uses the same value as the open password, so you can change permissions later with that one password. If you set a different owner password, give the open password to the recipient and keep the owner password for yourself.

That separation is a PDF convention, not a secure account system. Some tools do not enforce it, and if both passwords are the same, anyone with the open password can change permissions. Keep the owner password at least as safe as the open password.

Permissions: printing, copying and editing

Permission flags tell a PDF reader what it should allow. The tool maps your choices to QPDF's options:

• Printing: None blocks printing. Low resolution allows reduced-quality printing for previews. Full allows normal printing.
• Copying text and images: Allowed permits selection and extraction. Not allowed asks readers to block copying.
• Changes: None blocks editing. Fill forms allows form fields to be completed and saved. General editing allows broader page and content changes.

These are requests to the reader, not physical limits. Many viewers honour them, but some ignore them, and a recipient who can open the PDF may remove them with another tool. Encryption alone will not stop a determined person from copying a document.

AES-256 encryption

This tool asks QPDF to write AES-256 encryption, the strongest standard method in current PDF readers. The password is not stored in the file; QPDF derives a key from it and encrypts the contents. AES-256 resists brute-force attacks when the password is long and unpredictable, but the password remains the weakest point. A short or common password can be guessed, and an attacker with a copy of the file can try guesses offline.

Older PDFs may use weaker 128-bit or 40-bit encryption. This tool always writes modern 256-bit AES, so the copy may not open in very old software. Test it in the reader your recipient is likely to use.

What encryption does and does not protect

Encryption protects the contents of the PDF at rest and in transit. If the file is emailed, uploaded or copied, someone without the password should not be able to read it. It also sets the permission flags above.

It does not stop someone with the password from taking a screenshot, photographing the screen, printing or sharing the password. It does not stop a recipient using a tool that ignores permissions or removes them after opening the file, and it cannot protect a weak password from being guessed. File size and sometimes basic properties may still be visible; encryption is not anonymisation.

Think of it as a locked envelope, not a digital rights management system. It limits casual access and accidental disclosure, not a motivated recipient.

Losing the password

There is no recovery option. The tool does not store your password, and QPDF adds no backdoor. If you forget it, you cannot open the protected copy with this tool. Keep the original PDF until you have confirmed that the protected file opens with the password you chose. Store the password in a password manager and share it through a separate channel, not in the same email as the PDF.

When to use password protection

Use it when sending a contract, invoice, payslip, medical letter, draft report or other private document by email or file-sharing link and you want a basic extra barrier. It is also useful for an archive copy on a shared computer.

It is not a substitute for secure transfer, access control or legal confidentiality requirements. For highly sensitive material, use encrypted storage or a confidential-sharing service, and check your organisation's rules. Encrypt only documents you own or have explicit permission to protect; a password does not give you the right to distribute someone else's work.

Privacy and legal notes

The PDF is read and encrypted entirely in your browser. It is never uploaded to Lembog or sent to a third party. QPDF runs as WebAssembly; closing the tab discards the document.

You are responsible for the document and who receives the password. Encryption does not override copyright, confidentiality agreements, data-protection law or a court order. Do not use it to conceal material you have no right to share. Some organisations control encryption by policy, so check before protecting work documents.

Related PDF tools

• To add a visible signature, use Sign PDF. Add it before encrypting so the signature is included in the protected copy.
• To mark every page as confidential, use Watermark PDF.
• To reduce file size before sending, use Compress PDF. Compress first; an encrypted PDF must be unlocked before compression.
• To combine files into one protected document, use Merge PDF, then protect the merged file.

Protect PDF FAQ

Is this tool free to use?

Yes. There is no sign-up, watermark or page limit.

Are my PDFs uploaded to a server?

No. The file is read and encrypted by QPDF in your browser. Nothing is sent to Lembog or any third party.

What is the difference between the open and owner password?

The open password is required to view the PDF. The owner password is used to change permissions and security settings. If you leave the owner password blank, the open password is used for both.

Can I remove the password later?

Only if you know it. Open it in a reader that allows security changes and supply the owner password; if both are the same, that one works. This tool does not remove passwords, and there is no recovery if it is lost.

Do the permissions stop someone copying or printing?

They are instructions to the reader. Many viewers honour them, but some ignore them, screenshots work, and a recipient can use other software. They are not digital rights management.

What encryption is used?

Encryption uses AES-256, written by QPDF 12. Very old readers may not open it, so test with the recipient's software.

Can I protect a PDF that already asks for a password?

No. The tool must open the PDF to read its pages, so remove the existing open password first in a PDF reader using a copy you own, then protect the copy.

What happens if I forget the password?

There is no way to recover it. Keep the original and store the password safely before you delete anything.