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Protect a PDF with a password

This tool locks a PDF with a password, in your browser, so it cannot be opened without it. It uses AES-256, the strongest encryption the PDF format offers, applied on your device. Neither the file nor the password is uploaded.

or drop files here, or paste with Ctrl/Cmd+V

PDF · up to 50 files · 100 MB each

No file to hand?

Your files and password stay on your device. Nothing is uploaded. Check it yourself

How to use Protect PDF

  1. Add your PDFs

    Drop one or more PDFs on the box. Up to 50 files of 100 MB each.

  2. Choose a password

    Type it twice. Use at least 8 characters; a few unrelated words work well.

  3. Protect and download

    Press Protect PDF and save the locked copy. Keep the password somewhere safe.

How the password protection works

Protect PDF encrypts every text string and data stream in the file with AES-256. It runs in your browser. A PDF reader needs the password to work out the key and show anything at all; without it the content is unreadable data.

PDF files also carry an owner password, used for permission settings. PlumPDF sets a long random one and discards it; since no restrictions are set, it is never needed.

Your password is held in the page's memory only while the tool runs. It is never sent, saved, logged or included in analytics.

The original PDF is not changed. Text, images, links and bookmarks inside the protected copy are exactly as before, and the file size grows only slightly.

Questions about Protect PDF

How do I put a password on a PDF?

Add the PDF above, type a password twice and press Protect PDF. The copy you download asks for that password every time it is opened, in any PDF reader. Your original file is not changed.

How strong is the encryption?

PlumPDF uses AES with a 256-bit key, the method defined in PDF 2.0 and supported by all major PDF readers, current browsers and Preview on Mac. In practice the password is the weak point: a long password made of unrelated words is very hard to guess, and a short one is not.

What if I forget the password?

Then the file cannot be opened, by you or by PlumPDF. There is no recovery and no back door, which is the point of encryption. Keep the unprotected original, or store the password in a password manager.

Can I stop people from printing or copying instead?

Not with this tool. It sets an open password only, and anyone who has the password can print, copy and edit. Restrictions on printing or copying are honoured by some readers and ignored by others, so they are not real protection.

Can I protect a PDF that already has a password?

Remove the old password first with Unlock PDF, which needs it, then protect the result with the new one.

Can I protect several PDFs at once?

Yes. Add up to 50 PDFs and type the password once: the same password is set on every file, each encrypted with AES-256. Files that already have a password are skipped and listed. Download the protected copies one by one or as a zip.

Is it safe to password-protect a PDF online?

With PlumPDF, the file and the password stay in your browser tab. The encryption is done on your device. Nothing is uploaded, logged or stored.

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