To password protect a Word document, follow these steps:

1. Open the Word document you want to protect.
2. Go to the File menu and select Info.
3. Click on Protect Document and then choose Encrypt with Password.
4. Enter your desired password and click OK.
5. Re-enter the password to confirm it and press OK again.
6. Save the document to apply the password protection.

Once done, the document will require the password to open it. Passwords are case-sensitive and can be up to 15 characters long. Remember to save your password securely as it cannot be recovered if lost.