Password protect a PDF on iPhone

Lock a PDF in the Preview app with a password, keep a spare if you need one and know what a PDF password does and does not stop.

Steps

1. Open the Preview app on your iPhone.
2. Open the PDF. To keep a copy without a password, tap the More button and tap Duplicate before you go on.
3. Tap the arrow next to the filename, then tap Lock.
4. Enter the same password in Password and Verify. Require Password turns on by itself.
5. Confirm the change.

Apple’s page describes the lock as preventing others from editing or deleting your work. In practice, once Require Password is on, the file asks for the password to open. Test yours by closing and reopening the file.

Pick a real password

A PDF can be copied and attacked on a computer at any speed, so a short password offers little. The passphrase generator can make one in your browser. Six random words is a good target. Write it down somewhere safe.

Clean up after

The unlocked version may still sit elsewhere. Check:

• The location you scanned or downloaded it to
• Mail attachments and Sent
• Messages threads
• iCloud Drive, if you stored it there too

When a PDF lock is the wrong tool

Locking files one by one gets tedious beyond a handful. Backroom keeps any file type in an encrypted vault behind a single pattern, including PDFs you import from Files. The two can work together: lock a PDF and store it in a vault, if you want it protected even after you share it.