Password protect PDF files so only the people you choose can open them
Add a password a reader needs before they can open the PDF. The file is encrypted with AES-256 on this device, and neither it nor the password is uploaded.
Choose a PDF file to lock
One file · up to 80 MB · PDF bytes are checked on this device
Processed on this device
Selecting and processing files stays in this browser.
Checking offline readiness
Offline availability is confirmed after this tool loads.
Why there is no daily limit, and no upload
How to password protect a PDF
- Open the PDF you want to lock.
- Type the password twice, and choose what a reader may still do once it is open.
- Select Lock this PDF, then Download.
AES-256, applied on your own device
PDFCheetah encrypts the document with AES-256 — revision 6 of the PDF standard security handler, the same scheme Acrobat writes — using the encryption built into your browser. The file never leaves your device and neither does the password. Before the download appears, PDFCheetah opens the locked file again here and checks that the password really does open it, so a file that could not be unlocked is never handed to you.
Nobody can recover the password
There is no account, no upload and no copy of your key, which is the point — and it means a forgotten password cannot be reset by us or by anyone else. Write it down before you download the file.
What the permissions actually do
Printing, copying and editing restrictions are recorded inside the PDF, and mainstream readers honor them. They are a request rather than a lock: a reader that already has the password can choose to ignore them. Only the password decides who can open the document at all. Reading with a screen reader stays permitted whatever else you switch off.
Current limitations
A PDF that already has a password cannot be locked again here — remove the existing one first. Certificate-based security is not supported, and neither is setting a separate owner password, so anyone who has the password can open the file and remove the permissions with it. Always verify signed, certified, tagged, form-heavy, or archival PDFs in the reader used by the recipient.
Common questions
- Is my PDF uploaded to add a password?
- No. The document is encrypted in your browser and saved on this device. Neither the file nor the password is ever sent anywhere, which is also why nobody here can recover the password for you.
- What encryption does PDFCheetah use?
- AES-256, written as revision 6 of the PDF standard security handler — the scheme Acrobat and other current readers write. The encryption itself is done by the cryptography built into your browser rather than by code we wrote.
- What happens if I forget the password?
- The document cannot be opened, by you or by anyone else. There is no account, no upload and no copy of the key anywhere, so there is nothing to reset. Save the password somewhere safe before you download the file, and keep the original unlocked PDF until you have checked the locked one opens.
- Do the printing and copying restrictions actually stop people?
- They are recorded in the PDF and mainstream readers honor them, but the format cannot enforce them: a reader that already has the password can choose to ignore them. Only the password controls who can open the document at all. Reading with a screen reader stays permitted whatever else you switch off.
- Can I add a password to a PDF that already has one?
- Not here. Changing an existing password means removing the old one first, which needs that password — use Unlock PDF, then come back and set the new one. A PDF that already has a password is refused rather than locked twice.
- Will the locked PDF open in Acrobat, Preview and phone readers?
- AES-256 is supported by every current mainstream reader. Very old software that predates the PDF 2.0 encryption scheme may not open it. Check the file in the reader your recipient uses before you rely on it, as you would with any document you send.