AES-256 encryption in your browser — the file never uploads
| Level | Opens in | Status in 2026 | This tool |
|---|---|---|---|
| AES-256 (AESv3) | Acrobat 10+ (2010), all modern readers | Current standard | Default |
| AES-128 | Acrobat 7+ (2005) | Still sound; for old-reader compatibility | Via compatibility note below |
| RC4-128 | Acrobat 5+ (2001) | Cipher is broken — avoid | Not written |
| RC4-40 | Acrobat 3+ (1996) | Trivially decrypted | Not written |
| No password, restrictions only | Everything | Not secrecy — flags cooperative readers respect | Optional (owner password) |
The engine (qpdf) refuses to write RC4 unless explicitly forced — a deliberate safety in the library this tool is built on. AES-256 is the right default in 2026: every current reader opens it, and no reader too old to do so is still in serious use. If you must support a decade-old embedded reader, Acrobat's own "compatible with Acrobat 7" setting is the AES-128 route.
PDF encryption is real cryptography, not a lock sticker. When you encrypt a file, its streams and strings are enciphered with a key derived from your password, and the reader has to produce that key to draw page one. Get the password right and the document opens; get it wrong and there is nothing to open.
This tool runs qpdf compiled to WebAssembly — the same open-source engine behind several commercial PDF products — inside your browser tab. It writes AES-256 encryption with your choice of restrictions (the cryptographically enforced part is the open password; restrictions are flags honest readers obey). After writing, the tool re-opens the output to verify: encryption present, page count unchanged, key size correct. First use downloads ~2.2 MB of WebAssembly, cached afterwards; the tool then works offline.
A 3-page, 1,852-byte policy manual was encrypted with the password used in testing. The output came back at 2,665 bytes — 813 bytes larger, the overhead of the encryption dictionary and enciphered stream structure — reporting AESv3 with a 256-bit key. The verification pass confirmed: encrypted yes, 3 pages present with the password, both user and owner passwords matching what was typed. A deliberate wrong-password attempt on the same file failed with exactly the error every reader gives ("invalid password"), and decrypting with the right one returned the original 3 pages with title and author metadata intact. That round trip — encrypt, verify, fail closed on wrong input, decrypt cleanly — is the whole security model in one paragraph.
Open the PDF below, type a password, and hit Encrypt. The tool applies AES-256 encryption (the current PDF standard) locally in your browser and hands back a file that asks for that password on every reader. Free, no signup, no watermark, and the PDF never uploads — which is the point when the document is the sensitive thing.
The user password (open password) is what someone must type to open the file. The owner password is a separate master key for changing permissions. Encrypting with only an owner password produces a file that opens freely but blocks printing or copying — restrictions, not secrecy. This tool sets a user password by default and lets you set a different owner password for permissions management.
Yes — open the restrictions section before encrypting and uncheck printing, copying, or modifying. The output carries those flags, and honest readers (Acrobat, Preview, browsers) respect them. Be aware that restrictions are enforced by software cooperation, not mathematics: screen readers keep accessibility, and a determined user with free tools can strip flags. The open password is the cryptographically strong protection.
Strong. AES-256 is the same cipher used for government-grade data, and modern readers from Acrobat 10 onward open it natively. In a verified test, this tool's engine (qpdf) encrypted a 1,852-byte PDF into a 2,665-byte AESv3/256-bit file that reported 'invalid password' on a wrong attempt and opened correctly on the right one. The realistic risk isn't the cipher — it's a weak password, so use a long passphrase.
The content is untouched — same pages, same text, same images — but the file is rewritten: streams are encrypted, so the byte size shifts (in testing a 1,852-byte file became 2,665 bytes). If you later remove the password, everything readable comes back exactly as it was. One caveat: keep an unencrypted copy somewhere safe for yourself, because the password cannot be recovered from the file if you forget it.
No. The encryption engine is qpdf compiled to WebAssembly, running inside this page — the PDF is read, encrypted, and handed back to you entirely on your machine, and the tool keeps working offline once the engine has loaded. That matters more than usual here: files people want to encrypt are exactly the files they shouldn't hand to an unknown server.