If you want to add an extra layer of security to a PDF file before sending it via Gmail, password protection is a great way to ensure that only the intended recipient can access the document. Here's how you can password protect a PDF in Gmail:

1. Open the PDF file you want to protect.
2. Click on 'File' and then select 'Protect Using Password'.
3. Enter a password of your choice and confirm it.
4. Save the password-protected PDF file on your device.
5. Compose a new email in Gmail and attach the password-protected PDF file.
6. Send the email to the recipient and share the password with them through a secure channel.

By following these steps, you can ensure that your PDF file remains safe and secure while being transmitted via Gmail.