A family of Microsoft word processing software products for creating web, email, and print documents.
Please disregard the reply from LordAlukard: The links are to articles which pertain to Office on the Windows OS but even more significant is that you can't follow any of those steps since the problem is that the tool is unusable in the first place.
The most common reason is that the document currently in the foreground is in one of the older file types [such as .doc] which do not support the Add-Ins features. Is the document name in the title bar is followed by the Compatibility Mode notification? If you create a new blank document does the tool activate?