Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Its not any registration number that is required but the Office 2000 key, whch should be on a sticker fixed to the office cd case.
Not haveing the key, and office activated, should not prevent you viewing pre saved docs, it would only prevent creating new docs or editing old docs
What is the *exact* err msg you see