pdfcosmos

Protect PDF

Password-protect a PDF with AES-256 encryption, entirely in your browser.

Free, fast, and privacy-first.

Protect your PDFs with a password

or drag & drop files here

PDF files onlyup to 30 filesup to 100 MB each300 MB total

Password-protect a PDF with AES-256: free and private

Add a password to a PDF so only the people you share it with can open it, a natural fit for contracts, statements, and anything confidential. pdfcosmos encrypts the file with AES-256 entirely in your browser, so both the document and the password you set never leave your device.

Enter and confirm a password and the PDF is locked in seconds. Protect up to 30 files with the same password at once. One downloads as a protected PDF and several as a ZIP. Keep the password somewhere safe. The encryption is real, so a lost password can't be recovered. To take a password off later, use our Unlock PDF tool.

  • Real AES-256 encryption

    The current standard. Anyone opening the file will need the password you set.

  • Your password never leaves

    Encryption runs in your browser. Neither the file nor the password is sent anywhere.

  • Protect in bulk

    Apply the same password to up to 30 PDFs at once. Several download as a single ZIP.

  • Reversible when you know it

    Remove the password anytime with Unlock PDF. You just need the password you set.

How to password-protect a PDF

  1. Add your PDF(s)

    Drop one file (or up to 30) into the upload area.

  2. Set a password

    Enter and confirm a password, and the file is encrypted with AES-256, right in your browser.

  3. Download

    Click the button to encrypt, then download the protected file (a ZIP for several).

Frequently asked questions

Are my PDF or password sent to a server?
No. Encryption runs entirely in your browser using WebAssembly (qpdf). Your file and your password never leave your device. You can confirm it in your browser's Network tab: no data is sent.
How strong is the protection?
The PDF is encrypted with AES-256, the current standard. Anyone opening the file will need the password. Keep it somewhere safe. If you lose it, the file can't be recovered.
How do I remove a password later?
Use the Unlock PDF tool: enter the current password and it strips the encryption. (Removing a password always requires knowing it, and nothing can crack an unknown password.)
Can I protect several PDFs at once?
Yes. Add up to 30 PDFs and the same password is applied to each. One file downloads as a protected PDF. Two or more download together as a single ZIP.
Is Protect PDF free?
Yes, it's completely free to use, with no sign-up and nothing to install.