Password-protect a PDF
Add a password (AES-256) required to open the PDF, entirely in your browser. Nothing is uploaded.
How it works
- Add the PDF.
- Enter a password to open, and confirm it.
- Select Protect and review.
Limits
Processed locally on your device. Your file and password are never uploaded to SumoPDF, and SumoPDF does not receive or store them. Adds AES-256 "password to open" encryption with qpdf, entirely in your browser. This is a password to OPEN the file, not a permission/usage restriction and not a certificate or digital signature. SumoPDF CANNOT recover a lost password, so keep it safe. Beta limits: desktop up to 40 MB and 400 pages; mobile up to 15 MB and 150 pages. A PDF that is already password-protected must be unlocked first.
Common questions
How secure is the password I add to my PDF?
Your PDF is protected with strong AES-256 encryption, which is a standard for securing documents. Since the file is encrypted in your browser, the password you choose is never sent over the internet or seen by us.
Will the password I add work in other PDF readers?
Yes, the password protection is a standard feature of the PDF format. Anyone trying to open the file in another program, such as Adobe Acrobat Reader, will be required to enter the password you set.
Can I add a password to a large document?
You can add a password to any PDF up to 25 pages for free. For documents that are longer than 25 pages, a paid plan is required. The paid plan allows you to protect files of any size.
Can I remove a password later if I change my mind?
Yes, you can remove a password from a PDF as long as you know the correct password. You can use our Unlock PDF tool to create a new, password-free version of the document.
