These extensions can be viewed and managed from within each Office app, but if you’d just like a quick overview then it’s much easier to use NirSoft’s classic OfficeIns.
The program is tiny even by NirSoft standards – a 41KB download? really? – and portable, running happily on any Windows PC and with any version of Office released in the past 10 years or so.
On launch OfficeIns displays the usual NirSoft table with details on all your add-ins: name, description, developer, the Office app where it’s used (Word, Excel, Outlook etc), its Start Mode (load at startup or on demand), file name, Registry key and more.
Clicking on any column header sorts by that field, and just being able to do that may highlight some interesting details.
Clicking “Software” groups add-ins by their Office application, for example, which made it immediately obvious that our test system’s Outlook had more than its share (17), and that some references were for programs we’d removed (ESET’s uninstaller “forgot” to remove its Outlook add-in key, unfortunately).
If you do spot something you’re fairly sure is surplus to requirements, then try searching for its ProgID online, just to make sure it’s not doing anything important.
Ideally you should then disable or remove the add-in from its parent application, but if that’s not possible, right-clicking the entry in OfficeIns and selecting Change Start Mode > Disabled will prevent it from launching next time.
What you can’t do here is delete an add-in reference entirely, and on balance that’s probably a good thing. The risk of wiping something important far outweighs any reward.
But if you know what you’re doing, the program does have right-click options to open the add-in and CLSID keys in Regedit, where you can edit or delete them yourself.
OfficeIns is a freeware application for Windows 95 and later.