How to Password Protect a PDF
- Upload your PDF. Drag it into the box above or click to browse. The file stays on your device.
- Choose a password. Type the password anyone will need to open the document. Tap the eye icon to double-check it before you lock the file.
- Click Lock PDF. The document is encrypted with AES-256 on your own computer, in a fraction of a second.
- Download. Save the protected copy. When you or anyone else opens it, the PDF viewer will ask for the password first.
Why Password Protect a PDF?
A PDF often carries exactly the information you would least like a stranger to see: a salary slip, a tax return, a signed contract, medical results, a scan of your passport. The moment that file leaves your hands — attached to an email, dropped in a shared folder, sent over a messaging app — you lose control of where it ends up. A password puts that control back. Without it, the file is just scrambled, unreadable data.
Locking a PDF is useful any time a document is meant for specific eyes only. Sending an invoice to a client, sharing onboarding paperwork with a new hire, emailing a report to your accountant, or simply storing sensitive personal documents in the cloud — in each case a password means that intercepting or stumbling across the file is not enough to read it.
How Strong Is the Encryption?
This tool uses AES-256, the same encryption standard trusted by banks and governments and the strongest option the PDF format supports. When you set a password, the entire contents of the document are encrypted — text, images and metadata alike. There is no back door: the file can only be opened by someone who enters the correct password.
Because the strength of that protection ultimately rests on the password itself, choose one that is hard to guess. A short dictionary word offers little real security no matter how good the encryption is; a longer passphrase of several words, or a random mix of letters, numbers and symbols, is dramatically harder to break. If you need one, our Password Generator can create a strong password for you.
Is It Safe to Use?
Yes. Everything happens inside your browser using JavaScript and WebAssembly — the PDF and the password you type are never sent to a server and are never stored by us. This matters more than usual for a security tool: it would make little sense to protect a private document by first uploading the unprotected version to a stranger’s website. Here, that never happens. Once the page has loaded you can even disconnect from the internet and the tool still works.
Frequently Asked Questions
What happens if I forget the password?
There is no way to recover it. AES-256 has no back door, which is exactly what makes it secure — but it also means a forgotten password locks you out permanently. Write the password down somewhere safe, or store it in a password manager, before you lock an important file.
Will the person I send it to need special software?
No. Encrypted PDFs are part of the PDF standard, so any normal reader — Adobe Acrobat, Chrome, Edge, Preview on a Mac, or a phone’s built-in viewer — will simply prompt for the password when the file is opened. There is nothing extra to install.
Does locking change the contents of my PDF?
No. The pages, text, images and layout are untouched. The only change is that the file is now encrypted and asks for a password to open.
Can I lock a PDF that already has a password?
Not directly — a file can only hold one password at a time. If a PDF is already protected, unlock it first with our Unlock PDF tool, then lock it again with the new password.
Are my files uploaded anywhere?
Never. The document and password are handled entirely on your device and are never transmitted or saved. That is what makes this safe for genuinely sensitive files.
Related Tools
- Unlock PDF — the opposite: remove a password you already know
- Password Generator — create a strong password to protect your file
- Compress PDF — reduce a PDF’s file size
- Merge PDF — combine several PDFs into one