How to Password Protect a PDF (Free, on Any Computer or Phone)

A tax return, a signed lease, a scan of your driver's license. Some files should not be readable by whoever happens to see them, whether that is a coworker glancing at a shared folder or a stranger who gets hold of a forwarded email. Putting a password on the PDF is the simplest fix. Once it is on, the file shows nothing but a password prompt until the right password is typed. You do not need Adobe Acrobat for this, and it takes less time than writing the email you are about to attach it to. Below is the quick way, the built-in options on Mac and Windows, and the part most guides skip: choosing a password that actually holds up.

What a PDF password actually does

When you protect a PDF with an opening password, the file is encrypted. The text, images and form answers are scrambled with a key derived from your password. A PDF reader can only unscramble them after you type that password. This is different from a lock icon in a file-sharing app, which only controls who can download the file. Here the protection travels with the file itself, wherever it is copied, forwarded or uploaded.

There are two kinds of PDF password, and it helps to know which one you want:

• Opening password (also called a user or document-open password). Required to see anything. This is what most people mean by a password-protected PDF.
• Permissions password (also called an owner password). Lets people open the file but limits printing, copying or editing. We cover it in detail in our guide to restricting printing, copying and editing.

For keeping a document private, you want the opening password.

How to password protect a PDF in your browser (fastest)

This works the same on Windows, Mac, Chromebook, iPhone and Android, with no software to install.

1. Open Protect PDF and add your file. It is read in your browser, so it is not uploaded anywhere.
2. Type a password, then type it again to confirm. Tick Show password if you want to check for typos.
3. Leave the permissions section alone unless you also want to block printing or copying.
4. Click Protect PDF and download the file. It is saved with "-protected" added to the name.
5. Open the downloaded copy. It should ask for the password before showing anything.

The file is encrypted with AES-128, the standard that Adobe Acrobat, Preview on Mac, Chrome, Edge and phone PDF viewers all understand. The recipient does not need any special app to open it.

How to password protect a PDF on a Mac with Preview

Preview, the PDF viewer built into macOS, can add an opening password too.

1. Open the PDF in Preview.
2. On recent versions of macOS, choose File > Edit Permissions. Tick Require Password to Open Document, type the password and also set an owner password, which Preview asks for.
3. On older versions, choose File > Export, tick Encrypt and type the password twice.
4. Save, close the file and reopen it to make sure the password prompt appears.

The menu names have moved between macOS releases, so if you cannot find the option, the browser method above gives the same result.

How to password protect a PDF on Windows with Word

Windows has no built-in PDF tool that adds a password. But if your document started life in Microsoft Word, you can encrypt it at the moment you create the PDF:

1. In Word, choose File > Save As (or Export) and pick PDF as the file type.
2. Click Options.
3. Tick Encrypt the document with a password and click OK.
4. Type the password twice and save.

This only helps for documents you are writing yourself. For a PDF you received, a scan, or a statement downloaded from your bank, use Protect PDF in the browser instead.

Choosing a password that holds up

This is where PDF protection succeeds or fails. Anyone who has a copy of your file can try passwords against it on their own computer, as many times as they like, with no lockout after three wrong guesses. Cracking software can test millions of short passwords quickly. The encryption is strong. A weak password is the way in.

A few rules that make a real difference:

• Go long. Use at least 12 characters. Four random, unrelated words, such as tulip-garage-ninety-oven, are easy to type and very hard to guess. US guidance from NIST on passwords favors length over forced symbols for this reason.
• Do not reuse a password from your email, bank or any website. If that password ever leaks, your PDF is open too.
• Avoid the obvious. Birthdays, ZIP codes, the last four digits of an SSN and the recipient's name are the first things anyone would try.
• Use a new password per file or per recipient when the documents are sensitive. One leaked password then exposes one file, not all of them.

Before you protect: finish the file first

Once a PDF is encrypted, most tools can no longer change it until the password is removed. So do everything else first, in this order:

1. Remove what the recipient should not see with Redact PDF. A password stops strangers. Redaction stops everyone, including the person you send it to. Our guide on redacting SSNs and account numbers explains when you need which.
2. Combine and reorder pages if the file is made of several documents.
3. Shrink it with Compress PDF if it is going by email. An encrypted file cannot be compressed afterwards.
4. Sign it if a signature is needed.
5. Protect it last.

Keep a copy, and test it

Lost PDF passwords cannot be recovered. Not by us, not by Adobe, not by the person who made the file. There is no "forgot password" link, because there is no account behind it. Before you delete anything:

• Keep the unprotected original in a safe place, such as an encrypted drive or a folder only you can reach.
• Store the password in a password manager rather than in a note on the same computer.
• Open the protected copy once on another device, ideally a phone, to confirm the password works before you send it.

If the file is headed for someone else's inbox, how you share the password matters as much as the password itself. Our guide to emailing a password-protected PDF walks through it.

What a password does not protect against

Encryption keeps the file safe while it is stored or in transit. It does not control what happens after the right person opens it. They can save an unprotected copy, take a screenshot or forward the password. Password protection is also invisible to the file name, so a name like Smith-2025-tax-return.pdf still tells people what is inside. Give sensitive files a neutral name. Our guide on naming PDF files has a simple pattern.

Finally, be careful where you protect the file. A site that uploads your PDF to its server sees the document and the password together. Protect PDF runs entirely in your browser, which you can confirm with the checks in are online PDF tools safe?