Add a password to a PDF

Add a password to a PDF is useful when a document has to travel through email, shared drives or a messaging app. Because encryption here runs locally, the password has no server to be logged on — and that also means nobody can recover it for you.

Protect PDF — free and local

Adds AES-256 password protection plus printing and copying permissions.

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✓ Nothing is uploaded ✓ No watermark ✓ No signup

User password vs owner password

The user password is required to open the document at all. The owner password controls permissions: printing, copying text, editing. If you only set a user password, it doubles as the owner password, which is fine for most documents.

Set both when you want the recipient to read but not print or copy — for example a preview copy of a report. Permissions are advisory in the sense that a determined reader with the owner password can override them; treat them as a clear signal rather than a hard technical lock.

Why local encryption is the safer default

Every server-side "protect PDF" service receives your document and your password in the same request. Even with honest intentions, that is two sensitive things in someone else's logs. Here the AES-256 encryption happens with code already loaded in the page: no request is made during the operation.

You can verify it: open the browser network panel, encrypt a file, and watch that nothing leaves.

Practical advice on the password itself

Use at least 12 characters or a four-word passphrase. Short passwords on an encrypted PDF are brute-forceable offline — an attacker has the file and unlimited attempts. Avoid patterns like a client name plus the year.

Send the password through a different channel than the file: the file by email, the password by message or phone. One channel for both defeats the purpose.

Questions

What encryption is used?

AES-256, the modern PDF standard. The output opens in Acrobat, Preview, Chrome and every mainstream reader.

Can I recover a forgotten password?

No. The password never reaches a server, so there is nothing to recover and no backdoor. Save it before closing the tab.

Can I stop the recipient from printing?

Yes, via the owner password and the permission checkboxes. Note that permissions are advisory and can be overridden by a reader who has the owner password.

Password protect a PDF Encrypt a PDF with a password Lock a PDF with a password Compress PDF — Shrinks a PDF with four presets — lossless cleanup, light, balanced and extreme Compress to Size — Takes your upload limit in KB or MB and finds the best quality that still fits under it Merge PDF — Joins several PDFs into one document, in whatever order you choose Split PDF — Splits one PDF into page ranges or a single file per page, delivered as a ZIP

SlimPDF runs every tool in your browser. No file is ever uploaded, stored or shared.