Protect PDF

Add a password and permission controls to a PDF, in your browser.

Runs in your browser. Nothing is uploaded — your input is processed on this device and discarded when you close the tab.

Your file

Drop a PDF here or click to browse. One file at a time, up to 50 MB. Everything is processed on this device only — no file is uploaded, and your passwords are never sent anywhere.

User password (required)

Anyone opening the file must type this password. There is no recovery: if you forget it, the file stays locked.

Confirm user password

Owner password (optional)

The owner password controls the permissions below and can change them later. Leave blank to reuse the user password.

Printing Not allowed Low resolution only High resolution allowed

Allow modifying the document Allow copying text and images Allow comments and annotations

Permissions are requests that PDF readers are expected to honour. They discourage casual copying; they are not a substitute for the open password.

Encryption strength AES-256 (recommended, modern readers) AES-128 (older reader compatibility)

Protect PDF

Protect PDF adds real encryption to a PDF file: a user password that must be typed before the document opens, an optional separate owner password, and permission settings that tell readers whether the document may be printed, copied, modified or annotated. It is for anyone sending a contract, payslip, invoice, report or identity document who wants the file itself — not just the email around it — to resist casual opening and reuse.

Everything happens in your browser. The file is read from your device, encrypted in this tab with AES encryption, and handed back to you as a download. Your document and both passwords stay on your device: they are never uploaded, stored or logged, and the tool works the same with the network disconnected once the page has loaded.

How to use Protect PDF

1. Add your PDF. Drop the file onto the dropzone or click to browse. One file at a time, up to 50 MB. If the file is already password-protected, the tool says so — protecting it again is refused, because stacking a second password on top of the first only confuses recipients; unlock it first if you need to change its protection.
2. Set the user password. This is the password a reader must type to open the file at all. Type it again in the confirmation field; a mismatch is rejected before anything is encrypted. The strength hint updates as you type — a long phrase you can remember beats a short jumble you have to write down.
3. Set an owner password, or leave it blank. The owner password governs the permissions in the next step and can change them later in a full PDF application. Left blank, it simply reuses the user password.
4. Choose the permissions. Decide whether printing is off, low-resolution only, or high-resolution; and whether modifying, copying text and images, and annotating are allowed. These are the settings readers will be asked to respect once they are in.
5. Choose the encryption strength. AES-256 is the recommended default and opens in all current readers. AES-128 exists for compatibility with very old software.
6. Protect and verify. Click Protect PDF and the protected copy downloads with “-protected” added to its name; your original is never changed. Open the copy once and type the password yourself before you send it anywhere — this tool keeps no copy and offers no recovery, so this check is the only one that matters.

Features

• Real AES-256 encryption (with an AES-128 compatibility option), applied by the @cantoo/pdf-lib library running locally in your browser.
• Separate user and owner passwords, with a confirmation check on the user password and a live strength hint.
• Permission controls for printing (off, low-resolution, or high-resolution), modifying, copying and annotating, written into the document's encryption dictionary where readers look for them.
• Already-protected files are detected before you start and refused with an explanation, instead of being encrypted a second time.
• Your passwords are used only as arguments to the encryption running in this tab — there is no account, no upload and no server copy of anything.

Worked example

Take a three-page document whose pages are labelled MARKER-1, MARKER-2 and MARKER-3. Protect it with user password open-sesame, owner password owner-key, printing set to “Not allowed”, copying and modifying off, and AES-256. The result behaves exactly as the tests for this tool verify: a PDF reader refuses to open it without a password, refuses wrong-guess as incorrect, and opens it with either open-sesame or owner-key, showing all three pages with their text unchanged. Inside the file, the encryption dictionary records revision 6 (the AES-256 handler) and a permissions value that decodes back to precisely “no printing, no modifying, no copying, no annotating” — the settings landed, not just the password. Removing the protection again with the Unlock tool returns a three-page document with the same three markers, readable with no password at all.

Common errors and limitations

• Permissions are requests, not walls. The open password is enforced by encryption; the permission flags are instructions that compliant readers honour. A determined recipient with the user password can often bypass print or copy restrictions in other software. Set permissions to discourage casual misuse, not to guarantee it.
• There is no password recovery. If you forget the user password, this tool cannot help — nothing about your passwords ever leaves your device, and no copy of the file is kept. Store the password somewhere safe and test the protected copy before sharing it.
• AES-256 needs a reasonably current reader. Every mainstream reader of the last decade opens AES-256 files. If a recipient uses genuinely old software, choose AES-128 instead and accept its weaker protection.
• One file at a time, up to 50 MB. Protect files individually; a batch mode is not offered.
• A protected file cannot be protected again here. Files that already carry encryption — including files quietly encrypted by banks or scanners, sometimes with an empty user password — are detected and refused. Unlock first, then re-protect with the settings you actually want.
• Protection does not change content. Text, images, form fields and existing digital signatures are carried across unmodified; note that modifying a signed PDF in any tool can affect its signatures.

• Using the same password everywhere. If one file's password leaks, every file sharing it is open. Fix: use a distinct password per recipient or per document set, ideally a generated passphrase kept in a password manager.
• Sending the password in the same message as the file. An intercepted email then contains both the lock and the key. Fix: send the password through a different channel — a phone call or a separate message thread.
• Believing “no copying” makes the content uncopyable. Anyone who can read a document can photograph the screen. Fix: treat permissions as a courtesy barrier, share sensitive documents only with people you trust, and rely on the open password for the real protection.
• Forgetting to test the protected copy. A typo in the password field locks everyone out, including you. Fix: open the downloaded “-protected” file and type the password once yourself before sending it, every time.

Frequently asked questions

Related PDF tools

Prefer everything on one page? The original PDF Toolkit merges, splits and rearranges with one shared file list. The full suite is indexed on the PDF Tools hub.

How it works

Open the Protect PDF page and choose a PDF from your device, up to 50 MB. Everything runs in your browser: the file and the password you type never leave your device. You set a password that recipients must enter to open the document, choose AES-256 encryption — the recommended default, supported by all current readers — or AES-128 if a recipient uses genuinely older software, and set permissions for printing, copying text, and editing. The tool then builds a new, encrypted copy of the PDF for you to download. The original file is left unchanged, so keep it as your unprotected master copy. Share the password with recipients through a different channel from the file itself, such as a separate message, rather than sending both together.

Another worked example

Sam, a fictional freelance bookkeeper, needs to email a client's quarterly summary to that client. Sam opens the tool, selects the PDF, and sets a strong password the client can remember, with AES-256 encryption and copying and editing switched off. Sam downloads the protected file, emails it to the client at example.com, and sends the password separately by text message. The client opens the file with the password and reads it normally, while anyone who only intercepts the email attachment sees a locked document. Sam keeps the original unprotected file in a private folder, so the summary can be reissued without starting over.

More limitations to know

A lost password is unrecoverable: there is no reset, no back door, and no way to reopen a protected file without it, so store the password somewhere safe before you send the file. Protection raises the bar, but it does not stop a determined attacker — a recipient who can open the file can still photograph the screen, retype the contents, or use specialist tools to strip the protection. Permissions such as "no printing" or "no copying" are honoured by well-behaved readers, not enforced against every tool, so treat them as a request to honest readers rather than a lock. Finally, protection only covers the copy you send; any other copies already shared remain unprotected.

More frequently asked questions

Should the open password and the permissions be different?

They can be, and separating them is useful: one password opens the document, while a separate owner password can control permission changes. For most everyday sharing, a single strong open password is enough.

What if my recipient's reader is very old?

Choose AES-128 instead of AES-256 for that copy. It trades some strength for wider compatibility with older software, and it is still far better than sending the file unprotected.

Is it safe to email the password with the file?

No. If both travel together, anyone who gets the email gets both. Send the password through a separate channel, and confirm the recipient received it before deleting your note.

Does protecting a file change what is inside it?

No. The pages, text, and layout stay the same; only access to them is gated behind the password and the permissions you set.

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