How strong is the protection?

The cipher is AES-256, which is not the weak point of any real system. Your password is. A document locked with a dictionary word can be opened by someone working through dictionary words, so pick a long passphrase — several unrelated words beat a short string of punctuation.

Can you recover the password if I lose it?

No. Nothing about the password is stored in the file, and nothing about your file is stored here. A lost password means a document nobody will read again, including us. This is the honest consequence of encryption that actually works.

Why can I still not stop someone copying the text?

Because that restriction is a request recorded in the document rather than a mathematical barrier. Compliant readers honour it; other software ignores it. If text must not be readable by a particular person, the answer is to withhold the password from them, or to remove the sensitive part with the redaction tool before locking the file.

How do I send the password to the recipient?

By some route other than the one carrying the file. A password in the same email as the attachment protects against nothing, since anyone reading the message has both halves. A phone call or a separate messaging app is enough.

Protect PDF

Lock a PDF with a password and AES-256 encryption.

Everything runs inside your browser. Your files never leave your device.

Drop your files here

.pdf · they stay on this device

Ask about Protect PDF

Questions about what this tool does, which option to pick, or what it can and cannot handle.

This is the one part of the site that uses a server. The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong; the tool itself is not guessing.

About the Protect PDF

Putting a password on a PDF is the one thing in this whole toolbox where uploading the file to a website is not merely careless but self-defeating. The point of the exercise is that only people holding a secret should be able to read the document. Handing an unprotected copy, plus the secret, to a stranger's server first is a curious way to begin.

So this runs where it should: in your browser, with qpdf compiled to WebAssembly. Neither the file nor the password ever crosses the network.

The encryption is AES-256, which is the strongest thing the PDF format defines and the same primitive that protects a bank transaction. Weaker options exist in the specification — RC4 at 40 and 128 bits, both broken and both still offered by plenty of tools — and they are not offered here, because a lock that opens with a hairpin is worse than an honest absence of one: it invites the trust it cannot repay.

Two passwords can go on a document, and they do different jobs. The one you set to open the file is a real key. The optional second one governs whether the permission switches below can be changed, and it exists for a narrow case: sending a report that anyone may read but that your own department can still unlock and edit. Leave it blank and the opening password does both.

The permission switches deserve a candid description. Barring printing or copying is a flag inside the document, and readers honour it as a matter of convention. Adobe Reader and Preview will respect it. A determined person with different software will not, and cannot be made to. Treat those switches as a signpost, not a wall — the password is the part that actually holds.

Which brings up the only real danger here. A file encrypted with AES-256 and a lost password is gone. Not recoverable with effort, not recoverable with the right service: gone, permanently. Write the password down somewhere before you close the tab.

How to use it

1Drop in the PDF you want to lock. Several at once is fine — they all get the same password.
2Type the password that will be needed to open it, and store it somewhere safe first.
3Decide whether printing, copying text and editing should be permitted.
4Run the tool and download the encrypted file. Test it once by opening it before you send it on.

Questions

How strong is the protection?: The cipher is AES-256, which is not the weak point of any real system. Your password is. A document locked with a dictionary word can be opened by someone working through dictionary words, so pick a long passphrase — several unrelated words beat a short string of punctuation.
Can you recover the password if I lose it?: No. Nothing about the password is stored in the file, and nothing about your file is stored here. A lost password means a document nobody will read again, including us. This is the honest consequence of encryption that actually works.
Why can I still not stop someone copying the text?: Because that restriction is a request recorded in the document rather than a mathematical barrier. Compliant readers honour it; other software ignores it. If text must not be readable by a particular person, the answer is to withhold the password from them, or to remove the sensitive part with the redaction tool before locking the file.
How do I send the password to the recipient?: By some route other than the one carrying the file. A password in the same email as the attachment protects against nothing, since anyone reading the message has both halves. A phone call or a separate messaging app is enough.