How to password-⁠protect a PDF on iPhone

If you search the App Store for “lock PDF”, the top results are almost all $7.99-⁠a-⁠week scanner apps that upload your tax return or passport scan to their cloud server just to add a password.

Skip all of them. Apple builds native PDF password encryption straight into iOS inside the Files app and the system Print sheet (iPhone User Guide). It runs offline on your iPhone, costs nothing, and produces a standard encrypted PDF that opens on Windows, Mac, Android and iOS.

Two built-⁠in ways to password-⁠protect a PDF on iPhone

Method 1: Lock an existing PDF in the iPhone Files app

When your document is already saved as a .pdf file in Files (either in iCloud Drive or On My iPhone):

1. Open the Files app on your iPhone and tap the PDF document to open its preview.
2. Tap the file’s name (or the small down-⁠arrow chevron next to the title) at the very top center of the screen.
3. Tap Lock PDF from the drop-⁠down menu.
4. Enter a strong password, type it a second time in the Verify field, and tap Done in the top-⁠right corner to encrypt the PDF.

Once locked, the thumbnail in the Files app shows a lock icon and the text “This document is password protected”.

Method 2: Turn a photo, scan or webpage into a locked PDF (the Print trick)

What if you photographed a passport, driver’s licence, signed lease or medical bill in Apple Photos and want to email it as a password-protected PDF? Use iOS’s built-⁠in Print-⁠to-⁠PDF sheet:

• Open the photo (or select multiple photos) in Photos, or open the page in Safari or Mail, and tap the Share button.
• Scroll down the share menu and tap Print (you do not need a printer).
• At the top of the Print Options screen, tap the Share icon again.
• Notice the Lock PDF switch right below the PDF header at the top of the share sheet: switch Lock PDF on, enter and verify your password, and tap Save to Files (or send it straight to Mail or Messages).

Crucial cleanup step: if you created that locked PDF from a photo in Apple Photos, the original unencrypted photo is still sitting in your camera roll! Delete the original photo from Photos and empty Utilities > Recently Deleted, or move your stored ID scans into an encrypted vault app.

Why a PDF password must be much longer than a phone PIN

There is one major security difference between an iPhone lock screen and an emailed PDF file:

• On an iPhone lock screen, Apple’s Secure Enclave hardware chip enforces time delays and wipes/locks the key after 10 wrong attempts, so a 6-⁠digit PIN is protected by hardware rate-⁠limiting.
• An emailed PDF file has zero hardware rate-⁠limiting. Anyone who intercepts or downloads that PDF attachment can run offline GPU software that tests hundreds of thousands or millions of passwords per second (RFC 8018).

A 4-⁠digit PIN (0000–9999) or a 6-⁠digit birthday on a PDF cracks in less than one second. When locking a PDF that will travel over email or cloud storage:

1. Use at least 12 characters or 4 random words (for example maple-anklet-cobalt-49). Test how fast an offline attacker can guess a password in our unlock strength calculator.
2. Send the password over a different channel: if you email the locked PDF to your accountant or lawyer, send the password by Signal, iMessage or SMS, never inside the body of the same email as the attachment.
3. Rename the file before sending: PDF encryption hides the pages inside the file, not the filename in the email header. Name the file Document-2026-10.pdf rather than John-Smith-SSN-and-Passport.pdf.

For a complete guide to keeping ID cards, tax records and contracts safe on your phone day-⁠to-⁠day, see where to keep confidential documents on your phone.