Blog · Guide · September 27, 2026

How to password-protect a PDF on Windows (free)

A PDF of a contract, a payslip, medical results or an ID scan shouldn't sit unprotected on your PC or in an email. On Windows you can lock a PDF for free — here are the reliable ways, one big thing to avoid, and a stronger option that works for any file, not just PDFs.

Method 1: LibreOffice (free, any file you can open)

LibreOffice is free and can export a password-protected PDF from almost any document.

Open the document (or the PDF) in LibreOffice.
File → Export As → Export as PDF.
On the Security tab, click Set Passwords, enter an open password, and export.

Anyone opening the PDF now needs the password. Free, offline, no account.

Method 2: Microsoft Word

If your document is already in Word, you can export a locked PDF directly:

File → Save As, choose PDF as the type.
Click Options… and tick “Encrypt the document with a password.”
Set a password and save.

Method 3: Adobe Acrobat (paid)

Acrobat Pro can encrypt PDFs (Protect → Encrypt with password) with fine-grained permissions. It's powerful but a paid subscription — overkill if you just need to lock a file.

Avoid random "protect PDF online" websites. To add a password, they make you upload your document to a stranger's server — exactly the sensitive file you're trying to protect. You can't know what they keep. If a file is worth locking, don't hand it to an unknown site first. Do it on your own PC.

Method 4: Encrypt the file itself (strongest, any file type)

A PDF's built-in password is convenient, but its strength varies — older PDFs use weak schemes, and "PDF password remover" tools exist for a reason. For anything genuinely private, a stronger approach is to encrypt the file with modern encryption. That also works for photos, spreadsheets, ZIPs — anything, not just PDFs.

That's what Clavis does: it wraps the whole file in AES-256-GCM with a key derived from your password (Argon2id), on your PC. The result is a single locked file only your password can open.

With Clavis: drag your PDF in, press Encrypt, choose a strong password. You get one locked file. To read it, decrypt with your password. Nothing is uploaded, and it works the same for any file type.

Which method should you use?

Method	Cost	Best for
LibreOffice	Free	A password-locked PDF you'll share with someone
Microsoft Word	Paid (Office)	Documents you already edit in Word
Adobe Acrobat	Paid	Advanced PDF permissions
Encrypt the file (Clavis)	Free	Strong protection for private files of any type

Three habits that matter more than the method

Use a strong, unique password. A locked PDF with "1234" isn't locked.
Never send the password with the file. Share the file one way, the password another (e.g. a separate message or call).
Keep a way back in. If you forget the password, real encryption means the file stays shut — for you too. Note it in a password manager, or use a tool with a recovery key.

For a locked PDF you're emailing someone, LibreOffice is quick. For files you truly need private, encrypting the file itself is the stronger move — and Clavis does it in two clicks. See the Security page for the details.

Try Clavis — free for Windows