PDF lock

What a PIN on a PDF really protects, honestly

Locking a PDF with a password does one specific job: it stops the file from being opened casually. Mail the wrong attachment to the wrong person, leave a copy in a shared folder, lose a USB stick — with an open password on the file, the person on the other end sees a password prompt instead of your document. The encryption behind it here is AES-128, applied as the PDF standard's own open password, which every serious PDF reader understands. What it is not is an unbreakable vault: a four-digit PIN can be guessed by software given enough patience, so match the PIN to the stakes. For everyday privacy a short code is fine; for anything genuinely sensitive, use the Generate button with letters enabled and a longer length — every extra character multiplies the guessing work enormously.

Getting the PIN to the other person

The classic mistake is sending the locked file and its PIN in the same e-mail — anyone who has the mail has both. Send the file one way and the PIN another: file by e-mail, PIN by text message or a phone call. And write the PIN down before you close this page, because it is shown once and never stored anywhere — not by your browser, not by us. There is no recovery route by design: a lock we could undo for you would be a lock anyone could ask us to undo.

Locking things that are not PDFs yet

You can feed this tool an image or an Office document as well: a photo or scan is wrapped into a PDF page right in your browser, and Word or Excel files are converted on the server first, then locked. That makes it a quick way to protect a scanned contract or an ID photocopy before sending it anywhere. If you are bundling several documents, combine them first with the Merge PDF tool and lock the result once — one file, one PIN, one thing to keep track of.

How this works, and an honest limit

Word/Excel documents are converted to PDF first (the same engine behind Word to PDF); images become a one-page PDF right in your browser before upload. The PIN is then applied as a real PDF open-password (AES-128 encryption) — every common PDF reader will ask for it.

Honest limit: a small number of unusual, complex PDFs (heavy forms, certain scanners' output) can't be re-saved with a password by the engine this tool uses — you'll get a clear message instead of a broken file if that happens.