Password Protect PDF

No. The PDF is encrypted in your browser by QPDF running as WebAssembly in a background worker, and the protected copy is saved straight to your device. Your passwords are used only inside that worker, which is shut down as soon as the job finishes; they're cleared from the page afterwards and never stored or sent.

The file is encrypted with AES-256, the strongest standard PDF encryption (revision 6, defined in PDF 2.0 and supported by Acrobat X and later and by every current reader). Without the open password the pages, text and images can't be read. The weak point is the password itself: anyone who has the file can try guesses offline without limits, so use 12 or more characters, or four or more random words.

They tell PDF readers what to allow once the file is open: printing (full, low resolution or not at all), copying text and images, and editing (none, form filling, comments and forms, or anything). Adobe Acrobat, Preview, browsers and most other readers honour them, but they can't be enforced — the file has to be decrypted to be shown, and software that ignores the flags can print or copy anyway. Treat them as a polite request, and rely on the open password for confidentiality.

It's the PDF “owner” password. Entering it in an editor such as Acrobat lifts the restrictions or lets you change the security settings. It must differ from the open password. If you leave it blank, a long random one is used, so nobody can lift the restrictions with a password — keep your unprotected original if you might need changes later.

No. Nothing is stored anywhere, and AES-256 can't be bypassed — only guessing the password would work, which this site doesn't do. Keep the password in a password manager, and keep an unprotected original somewhere safe.

Yes. Open it here, enter its current password, then set the new password and permissions. The old encryption is replaced. To remove the password entirely, use Unlock PDF.

No. QPDF rewrites the same pages, fonts, images, links, bookmarks and form fields — it only adds encryption. The file size usually changes by a few kilobytes. Digital signatures in the original become invalid, because any re-save changes the signed bytes.

Up to 127 bytes: that's 127 plain letters, digits and symbols, while accented letters and emoji take 2–4 bytes each. Non-English characters work in modern readers, but some older apps can't type or accept them, so plain characters are safest for a file you send to others. Line breaks and tabs aren't allowed.

Open it as usual in Adobe Acrobat Reader, Apple Preview, a browser such as Chrome, Edge, Firefox or Safari, or another current PDF reader — it asks for the open password. PDF passwords are case-sensitive.

Not with this tool — it always sets an open password. Restrictions on their own can't be enforced, because the file has to open without a password, and many free apps ignore them. If you mainly want to discourage copying, a visible watermark is often more effective.

The contents are protected by AES-256, so the file itself can travel by email. Send the password a different way — by text message, phone or a chat app — not in the same email, and choose one that's hard to guess.