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A careful PNG-to-PDF or JPG-to-PDF workflow keeps page images on your device, preserves their intended order, and ends with a check of the finished document.
Read guide →Protect PDF with Password
Encrypt a PDF with 256-bit AES using qpdf compiled to WebAssembly, so neither the file nor the password reaches a server.
Drop a PDF here or click to browse
This PDF is processed in your browser and is not uploaded to opentools.
Reviewed 2026-08-15
Free Password Protect PDF – how it works
Encryption is handled by qpdf, the same library many command line workflows rely on, compiled to WebAssembly and run inside the page. The document is encrypted with 256-bit AES, which is the strongest scheme the PDF specification defines and the one current readers expect.
This is the part that matters when the file is sensitive: a server-side encryption service has to receive your unprotected document and your chosen password in order to do the work. Here both stay in the tab. The encrypted output is assembled locally and handed to your browser as a download.
If you leave the owner password blank it is set to match the user password. The user password is the one needed to open the document, so that combination is the straightforward "you need this password to read the file" setup rather than a permissions-only restriction that most readers ignore anyway.
How to use Password Protect PDF online
- Add the PDF. Drop in the document you want to protect. It must not already be encrypted; remove an existing password first if it is.
- Set the password. Choose a user password, which is what someone types to open the file. Set an owner password too if you want a separate credential for permissions, or leave it blank to reuse the user password.
- Encrypt and store the password somewhere safe. Run the encryption and download the result. There is no recovery path, so record the password in a password manager before you send the file on.
When to use it
- Protect a contract or payslip before emailing it as an attachment.
- Encrypt medical or financial records that are being shared outside an organisation.
- Add a password to a document going into shared cloud storage.
- Restrict a draft so only intended reviewers can open it.
Known limitations
- A lost password cannot be recovered. AES-256 encryption is not reversible without the credential, and opentools keeps no copy of it.
- Encryption protects the file, not the content once it is open. Whoever has the password can copy, print, or screenshot the pages.
- Already encrypted PDFs need decrypting first. Run Remove PDF Password before adding a new one.
Frequently asked questions
How strong is the encryption?
It uses 256-bit AES, the strongest option in the PDF specification, applied by qpdf. A password of reasonable length and randomness is not feasible to brute force; a short dictionary word is, so the password you choose matters more than the cipher.
Is my PDF uploaded anywhere?
No. The document is processed by WebAssembly and JavaScript running inside the page, so the bytes never leave your device. There is no upload step and nothing to delete afterwards.
What is the difference between the user and owner password?
The user password is required to open the document. The owner password governs permissions such as printing and editing, and can bypass those restrictions. Leaving the owner field blank sets it to the user password.
Can I recover the file if I forget the password?
No. Nothing about the document or the password is stored anywhere, and the encryption has no back door. Save the password before you distribute the file.
Will the protected PDF open in any reader?
Yes, in any reader that supports AES-256, which covers current versions of Acrobat, Preview, Chrome, Edge, and Firefox. Very old readers predating the standard may not open it.
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