How do I turn off Copilot in Word documents?

You can do it the hard way by simply cutting off MS Word from the Internet:

Just block MS Word in Windows firewall advanced settings:

Search Windows Defender Firewall with Advanced Security in the Windows Start menu

Create a new outbound rule

Select "Program"

Search the Microsoft Word executable on your machine using the "Browse" button and enter the corresponding file path

Select "Block the connection"

Enable the new rule for all network domain options

Provide a decent name for the new rule

NB: You must be Local Administrator on your machine to be able to edit firewall settings