Protect PDF

Protect PDF puts a password on a PDF before you email it, share it in a cloud folder or leave it on a shared computer. Payslips, contracts, medical letters, ID scans and client reports are the usual candidates. Once locked, the file’s contents are scrambled with AES-256, the strongest option in the PDF standard, and every normal reader — Adobe Acrobat, Preview, Chrome, Edge, phone apps — asks for the password before showing a single page.

You can also go further, or lighter. A separate permissions password lets you block or limit printing, copying, editing, comments, form filling and page changes. Or choose “Restrictions only” for a file anyone can open but not easily print or copy, such as a draft you want people to read but not reuse.

Locking a file with an online service means handing over the very document you want to keep private. Here the encryption runs in your browser: the PDF and both passwords stay on your device. Before the download is offered, the new file is opened by a second PDF reader to prove it refuses to open without the password and opens with it.

1. Tap “Choose a PDF” or drop one file onto the box.
2. Type a password in “Password to open”, or press “Suggest a strong one”. Watch the strength meter, then type it again in the second box.
3. Optional: open “Also restrict printing, copying and editing”, set what people may do, and add a permissions password.
4. Press “Protect PDF”. The tool encrypts the file and checks the result.
5. Press “Download PDF”, and keep the password somewhere safe.

• AES-256 encryption (the PDF 2.0 standard handler) for every file — no weaker options to pick by mistake.
• Live strength meter that spots common passwords, years, keyboard runs and repeats, with a rough guessing time.
• Show/Hide buttons, a confirm box that tells you as soon as the two match, and a random password generator with a copy button.
• Optional permissions: printing at full quality, low quality only or not at all; copying; editing; comments; form filling; adding, removing or turning pages.
• “Restrictions only” mode for files anyone may open but not freely print or copy.
• A blank permissions password becomes a long random one, so the open password alone can’t lift your restrictions.
• Screen-reader access is always left on, so the locked file stays usable for blind and partially sighted readers.
• The finished file is re-opened by a different PDF engine to confirm the lock works before you download it.
• Pages, text, links and form fields are kept exactly; nothing is redrawn or turned into images.

• Length beats cleverness: three or four unrelated words with a number between them is stronger and easier to remember than a short jumble.
• Send the password a different way from the file — a text message or a call, not the same email thread.
• Print, copy and edit restrictions only stop people using well-behaved apps. For anything truly private, rely on the open password.
• Do any merging, compressing, signing or watermarking first. Locked files have to be unlocked before other PDF tools can work on them.
• A file that is already locked can’t be locked again here; remove the old protection with Unlock PDF first, then set the new one.