Password protect a PDF
Choose a password and CLEKARA encrypts the document with 256-bit AES right here. Without that password nobody can open it, and your file and password never leave this device.
Drop the PDF you want to protect
or pick one or more files from your device
- Open one PDF or several. They will all be protected with the same password.
- Type a password and repeat it, or press Generate a strong password. The meter tells you how hard it is to guess. If you want, open Permissions to block printing, copying or editing.
- Press Protect PDF and download the result. Save the password somewhere safe: it cannot be recovered.
Real encryption, not just a lock icon
CLEKARA uses the standard security handler of PDF 2.0 with 256-bit AES — what Adobe Acrobat calls “256-bit AES” encryption. A random key is generated for the document, every page, image, font and piece of text is encrypted with it, and that key is itself locked with your password through a deliberately slow hash that combines SHA-256, SHA-384 and SHA-512. Even the document's title and author are encrypted.
Before the download appears, the protected copy is opened again in your browser: it must open with your password, have the same number of pages, and refuse to open without it. If any check fails, no file is offered.
Everything happens in this tab with your browser's own cryptography (Web Crypto). There is no server copy of the file and no copy of the password: CLEKARA never sees either.
Good to know
There is no way to recover a forgotten password — that is the point of encryption. Copy it from the result screen into your password manager.
AES-256 PDFs open in Adobe Acrobat and Reader (version X or later), Chrome, Edge, Firefox, Safari, Preview, Foxit, and the PDF viewers on Android and iPhone. Very old viewers from before 2010 may not open them.
Permissions such as “no printing” are honoured by Acrobat, browsers and most viewers, but they are a rule the viewer agrees to follow, not encryption; some programs ignore them. The password to open is what actually keeps people out.
PDFs that are already password protected must have their protection removed first. Encrypting a PDF that carries a digital signature rewrites the file and that signature stops validating; CLEKARA warns you when it finds one.
Frequently asked questions
How do I put a password on a PDF for free?
Open the PDF here, type the password twice and press Protect PDF. It is free, with no account and no watermark.
How secure is it?
It uses 256-bit AES, the strongest encryption the PDF format defines and the same one Adobe Acrobat uses. With a long, random password, guessing it is not practical. A short or common password, on the other hand, can be guessed, which is why the meter warns you.
Is my file or password uploaded?
No. The file is read, encrypted and checked inside this browser tab. Neither the document nor the password is sent anywhere.
Can I stop people from printing or copying my PDF?
Yes. Open Permissions and choose what to block. You can even leave the password to open empty and only limit printing or copying.
Can I protect several PDFs at once?
Yes. Add them all and they are encrypted with the same password; you can download them one by one or together in a ZIP.
I forgot the password. Can you recover it?
No. CLEKARA never sees your password and the encryption is designed so that it cannot be bypassed. Keep a copy of the original file until you have saved the password.