How to Protect a PDF Document with a Password (Mac, Windows, and Mobile)

If you run a small business, you send sensitive files every week. Tax documents go to your accountant. Vendor contracts go out for review. Client invoices go out for payment. Sending these files as open attachments leaves your data exposed if an email is forwarded to the wrong person or intercepted.

You need a document lock. Putting a password on a PDF ensures only the intended recipient can view the contents.

Here is exactly how to protect a PDF document on your computer using built-in tools, and how to lock files directly from your phone when you are away from your desk.

Open password vs restrictions: what is the difference?

PDF security has two separate parts, and most confusion comes from mixing them up.

The open password (sometimes called the user password) encrypts the document. Without the password, a reader app cannot show the pages at all. This is the right choice for payslips, medical letters, ID scans and anything else where the content itself is private.

Restrictions (set with what is often called the owner or permissions password) let anyone open and read the file, but tell the reader app to switch off certain actions, such as:

• changing the content, adding comments or filling in forms
• copying text and images
• printing, or printing only at low quality

The important detail: a restriction is an instruction to the app. Well-behaved PDF readers follow it, but nothing forces every app to. Some apps simply ignore it, and tools exist that remove restrictions from a PDF that opens without a password. So restrictions are useful to stop casual edits and accidental changes, but they will not stop someone who is determined to copy your text. If that matters, add an open password and only share it with the right people.

You can use both at once: an open password for privacy, plus restrictions for the people who do have the password.

Method 1: How to Password Protect a File on Mac (Using Preview)

If you use a Mac, you do not need third-party software to lock a PDF. Apple’s built-in Preview application handles standard encryption.

1. Open your PDF using Preview.
2. Click File in the top menu bar, then select Export.
3. At the bottom of the export window, check the box labeled Encrypt.
4. Enter your chosen password, then verify it in the second box.
5. Click Save.

The new file is now secured. Anyone who opens it will face a prompt asking for the password.

Method 2: How to Protect a PDF Document on Windows (Using Microsoft Word)

Windows does not have a built-in PDF reader that applies passwords. However, if you have Microsoft Office installed, you can apply a document lock during the save process using Microsoft Word.

1. Open your document in Microsoft Word.
2. Click File, then Save As.
3. Choose PDF from the file format dropdown menu.
4. Click the Options button below the format selector.
5. Check the box for Encrypt the document with a password and click OK.
6. Type your password, confirm it, and save the file.

This method works well if you are creating the document from scratch. If you are trying to lock an existing PDF that you did not create, you will need a dedicated PDF tool.

Using Web Converters (And Their Trade-Offs)

If you search for how to lock a PDF, you will find web tools from Adobe, Smallpdf, and Canva. These platforms work well on a desktop computer. You upload your file, enter a password, and download the locked version.

The trade-off is the account requirement. Many web-based PDF editors put encryption tools behind a login screen or a premium paywall. If you are on your phone at an airport trying to send a secure invoice, typing credit card details or verifying a new account email is a massive block to your workflow.

How to protect a PDF in your browser with Filo

Filo's Protect PDF tool works on Windows, Mac, Chromebook, iPhone and Android, in a current version of Chrome, Edge, Firefox or Safari. The PDF is encrypted in your browser, so neither the file nor the password is uploaded.

Step 1: Open the PDF

Go to Protect PDF and drop your PDF onto the page, or pick it from your files.

Step 2: Choose a password, restrictions, or both

• Password: type it twice if you want the file to ask for a password before it opens. Use at least 6 characters; a longer password that is not a word or a date is much stronger.
• • Block editing: changing the content, adding comments, filling in forms and adding or removing pages.
  • Block copying text and images: screen readers can still read the text aloud, so the document stays accessible.
  • Block printing, with an extra option to Allow low-quality printing only.

The open password is optional when you set a restriction. If you only tick restrictions, anyone can open and read the copy, and the restrictions apply to everyone who gets it. As the tool itself says, most PDF readers honour these restrictions, but some apps ignore them, so they do not replace a password.

Step 3: Download

Save the new PDF. It is encrypted with AES-256 and carries your password and restrictions. Open it in your usual reader to check that it behaves as you expect.

A few honest details:

• Filo does not keep your password. Without it, nobody can open a password-protected copy, so keep your original file, or store the password somewhere safe.
• Keep an unprotected original for your own future edits, especially if you only set restrictions.
• On the web you get 3 free conversions in total, and files made with a free conversion carry a small Filo mark in the corner. The Filo app for iPhone and Android is free for life, with no daily limit.

Use It Now: How to Lock a PDF on Your Phone with Filo

If you need to secure a file from your phone (or if you need to batch protect multiple files), Filo handles this directly on iOS and Android. There is no account to create.

Note: Filo image tools function completely offline. Some Filo PDF tools, including PDF-to-Word conversion, require an active internet connection: the file goes through a secure server pass and is deleted when the conversion finishes.

• Step 1: Open the Filo app and tap Lock PDF. 
• Step 2: Select the PDF file (or multiple files) from your phone’s storage. 
• Step 3: Enter the password you want to apply. 
• Step 4: Tap Protect. 
• Step 5: Save the secured file or share it directly to your email app.

Bonus Workflow: Converting PDF to DOC Before Locking

Sometimes you receive a contract that needs a quick text adjustment before you lock it and send it back. Filo includes a PDF to Word tool for this exact scenario.

1. Tap PDF to Word in the Filo app.
2. Select your PDF. The app converts it to a DOC file you can type on.
3. Make your text edits.
4. Export the file back to PDF.
5. Run it through the Lock PDF tool to secure it.

This keeps your entire document workflow in one app on your phone. Filo is free to download with premium via subscription.

Tips for sharing a protected PDF

• Send the password separately. If the password is in the same email as the attachment, anyone who gets the email gets both. A text message or a phone call is better.
• Hide what should never be seen. Restrictions and passwords protect the file, but once someone can open it, they can read everything in it. If a page holds an account number or a signature the reader does not need, black it out first with Redact PDF, which removes the content under the box rather than just covering it.
• Test in more than one app. Because some apps ignore restrictions, open your protected copy in a second reader before you rely on it.
• Need to remove protection later? If you know the password, Unlock PDF saves a copy that opens without it. It never guesses or cracks passwords. Note that it can also lift restrictions from a PDF that opens without a password, which is a good reminder of how light that kind of lock is.

Quick Answers About PDF Protection

Secure Your Files From Anywhere

Leaving financial documents and contracts unprotected is a risk you do not have to take. If you are at your computer, use Mac Preview or Microsoft Word to encrypt your files.

If you are away from your desk and need to secure a document fast, use Filo. You can lock PDFs, convert them to Word for quick edits, and send them to clients safely. Filo is free to download with premium via subscription on iOS and Android. No account to create, no complicated menus.

Sources checked

• Apple Support: Password-protect a PDF in Preview on Mac, checked 12 November 2026
• Microsoft Support: Save or convert to PDF or XPS in Office desktop apps, checked 12 November 2026