How to Password-Protect a PDF

Removing restrictions is only half the story of PDF security, sometimes you need to add them. Whether you're emailing a contract, sharing payroll data, or sending a draft you don't want edited, a password keeps the file in the right hands. This guide covers three ways to protect a PDF (paid and free), explains the two password types, and offers a few rules for choosing a password that actually holds up.

Two protections you can add

• Document Open (user) password: Encrypts the file so it cannot be viewed without the password. This is the real security, backed by AES encryption.
• Permissions (owner) password: Lets anyone open the file but restricts printing, copying, or editing. Useful for "view only" distribution, though determined users can strip these flags, so it's a deterrent rather than hard security.

For confidential material, always use a Document Open password. For "please don't edit this," a permissions password is enough. See how PDF encryption works for why the open password is the one that matters.

Method 1: Adobe Acrobat Pro

1. Open the PDF and choose Tools → Protect → Encrypt → Encrypt with Password.
2. Confirm you want to change security on the document.
3. Tick Require a password to open the document and enter it, or set Permissions restrictions with an owner password, or both.
4. Choose the compatibility level (Acrobat X and later uses AES-256, the strongest option).
5. Click OK and save the file.

Method 2: macOS Preview (free)

1. Open the PDF in Preview.
2. Choose File → Export (hold Option and use "Export as PDF" if needed).
3. Tick Encrypt, enter and verify a password.
4. Click Save. The exported file now requires the password to open.

Method 3: LibreOffice Draw (free, Windows/Linux/Mac)

1. Open the PDF in LibreOffice Draw.
2. Choose File → Export as → Export as PDF.
3. On the Security tab, click Set Passwords.
4. Enter an open password and/or a permissions password, then export.

When you should protect a PDF

• Sending personal or financial data (tax forms, medical records, payslips) by email.
• Distributing a document you want read but not altered or reprinted.
• Archiving sensitive records that others share a device or drive with.
• Sending drafts to clients where an edited copy could cause confusion.

A password is only as safe as how you share it: send it through a different channel than the file itself, and store it in a password manager. For more on secure delivery, see sharing sensitive PDFs securely.