Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
I have a suggestion that involves changing your privacy settings. It does not remove the Copilot menu item on the ribbon, nor does it remove the initial line about Copilot when you create a new document. But it prevents your doc from using Copilot. At least it worked for me.
In Word, go to File > Options > General.
Click Privacy Settings.
Scroll down the dialog and UNcheck one or both of the boxes in "Connected Experiences". I have the first box unchecked, and this makes Word lose access to Copilot.
Given other comments, I would like to re-iterate that my solution does NOT remove the new Copilot item on the ribbon. It does NOT remove the initial Copilot line you get in a new document. But it DOES stop Word from accessing Copilot.