How do I password protect a PDF for free?

On Mac, open the PDF in Preview, go to File, Export as PDF, click Show Details, then set a password under Security Options. On Windows, open the source document in Microsoft Word, go to File, Save As, click Options under the format dropdown, and set a password before exporting to PDF. Adobe Acrobat online is a free browser option with a daily limit.

How strong is a PDF password?

Modern PDFs use AES-256 encryption when password protected. A strong, unique password provides solid protection. However, if the PDF is shared with someone who uses a PDF password removal tool, a weak password can be cracked. Use a long, random password for sensitive documents.

Can I password protect a PDF without Adobe Acrobat?

Yes. On Mac, use Preview's built-in Export as PDF security options. On Windows, LibreOffice (free) can set a PDF password on export. Adobe Acrobat online also offers a free tier. Microsoft Word can set an open password before exporting to PDF.

How to Password Protect a PDF Free (Windows, Mac, Online)

May 2026 · 4 min read · Last updated: May 2026

Adding a password to a PDF prevents unauthorised people from opening it. This matters for financial statements, legal documents, personal records, or any file you need to send over email but do not want freely readable if it ends up with the wrong person.

Here are four free methods, one for each platform, with no software purchase required.

Why Password-Protect a PDF

Sending payslips, bank statements, or tax documents by email
Sharing medical or legal records where access should be controlled
Protecting client files or confidential business reports
Meeting compliance requirements that mandate encryption for personal data in transit

Method 1: Microsoft Word (Windows and Mac)

Windows / Mac

1 Set a password during PDF export from Word

Best for: Documents you are creating or editing in Word before sharing

Open your document in Microsoft Word
Go to File and select Save As
Choose PDF as the format
On Windows: click Options in the save dialog, then check Encrypt the document with a password and enter your password
On Mac: click the dropdown that says Best for printing online and select Best for electronic distribution, then look for Security Options
Click Save

The resulting PDF will require the password to open in any PDF viewer. Word's PDF export uses AES-128 or AES-256 encryption depending on your version. This is a reliable method for documents you start in Word.

Keep a record of your password. There is no recovery option. A forgotten password means the PDF cannot be opened again.

Method 2: Mac Preview (No Extra Software)

Mac

2 Set a PDF password in Preview when exporting

Best for: Mac users with an existing PDF they want to protect

Open the PDF in Preview
Go to File and select Export as PDF
Click Show Details to expand the options
Click Security Options
Check Require password to open document
Enter and confirm your password
Click OK, then Save

Preview's security options let you set separate passwords for opening and for editing. For most uses, only the opening password is needed. This method is completely offline and free on every Mac.

Method 3: Adobe Acrobat Online

Any browser

3 Protect PDF using Adobe Acrobat online

Best for: Users who already have a PDF and need to add a password

Go to acrobat.adobe.com
Select Protect PDF from the tools list
Upload your PDF
Enter your password and confirm it
Click Set password and download the protected PDF

Adobe's free tier allows a limited number of operations per day. Your file is uploaded to Adobe's servers for processing. For truly sensitive documents, the offline methods (Preview on Mac, Word on Windows, LibreOffice) keep your file off the internet.

Method 4: LibreOffice (Free, Cross-Platform)

Windows / Mac / Linux

4 Export with password from LibreOffice

Best for: Users without Microsoft Word who need an offline solution

Download and install LibreOffice from libreoffice.org (free)
Open your document in LibreOffice Writer
Go to File and select Export as PDF
Click the Security tab in the PDF export dialog
Click Set open password and enter your password
Click Export

LibreOffice is a fully featured free office suite that handles Word documents well. It uses AES-256 encryption for PDF passwords. This is a good permanent solution for anyone who does not have Microsoft Office.

An Important Note About PDF Passwords

PDF passwords are not unbreakable. A password-protected PDF with a weak or short password can be cracked with readily available software. For documents requiring strong protection, use a long random password (12+ characters) and share the password through a separate secure channel, not in the same email as the PDF.

For truly sensitive data such as medical records, legal documents involving personal identification, or financial records with full account details, consider whether email is the right channel at all. Secure file transfer services or encrypted messaging may be more appropriate.

About Our Tools

Password protection requires writing an encrypted file, which is a different technical operation from the conversion and manipulation tools we currently offer. For password protection, Mac Preview and Adobe Acrobat online are your best free options. We are being upfront rather than directing you to a tool that does not meet your need.

What we can help with once your document is ready:

The PDF is too large to email: use our compress PDF tool to reduce the size first
You need to combine multiple PDFs before protecting: use our merge PDF tool to join them first, then add a password