Hi George Lau,
It is understandable that you would want to protect the document after working on it for several days.
Before trying any Copilot or license troubleshooting, please keep the document open and use File > Save a Copy to save it under a new name. If saving to the current location does not work, try another location such as OneDrive or your Desktop.
It is not yet clear whether the Copilot access problem and the document-saving problem are connected. Could you let me know which Microsoft 365 app you are using, what happens when you try to access Copilot, and the exact message shown when the document fails to save? Please remove any personal information from the screenshot or error details before posting them. Thank you so much for your understanding.
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