How to Password Protect a PDF

Email is not a secure channel. Messages pass through several servers, get forwarded, and sit in inboxes for years. Adding a password to a PDF means that even if the file ends up in the wrong place, it cannot be opened without the password.

It is worth protecting any PDF that contains personal or financial information: tax returns, payslips, bank statements, medical records, contracts, ID copies and client data.

Protect PDF encrypts the document in your browser. Neither the file nor the password is uploaded to PDF Utility.

1. Open Protect PDF and select your document.
2. Enter a password, then type it again to confirm it.
3. Encrypt the PDF and download the protected copy.
4. Open the protected file once to confirm the password works before you send it.

Protect PDF uses AES-256 encryption, the strongest standard encryption defined for PDF files. It is supported by modern readers including Adobe Acrobat and Reader, Preview on Mac, and the PDF viewers built into Chrome, Edge and Firefox.

Encryption is only as strong as the password. AES-256 does not help if the password is 1234 or the company name. A long, unique password makes the file practically impossible to open without it.

• Use at least 12 characters. A passphrase of four or five random words is long and easy to type.
• Avoid names, birthdays and words related to the document's content.
• Use a different password for each recipient or batch of documents.
• Store it in a password manager. PDF Utility does not keep a copy and cannot recover it.

Never send the password in the same email as the PDF. Anyone who gets the email gets both. Send the password by another route: a text message, a phone call, a messaging app, or an agreed password you set up in advance.

Microsoft Word can encrypt a PDF when you save it: choose Save As, select PDF, open Options and enable encryption with a password. On a Mac, Preview can add a password from its export and permissions options. These work if you already have the software; Protect PDF works on any device with a browser.

A password controls who can open a file, but anyone with the password can read everything in it. Remove pages the recipient does not need with Delete PDF Pages before protecting it. To discourage onward sharing, add a watermark with the recipient's name or CONFIDENTIAL first, then protect the watermarked copy.

If you later need an unprotected copy, use Unlock PDF with the current password.