Add-ins are tools you can build to customize and extend any Microsoft Office 2000 application. Add-ins perform specific tasks and are usually accessed through a menu command or a toolbar button. Add-ins can also perform tasks in the background, responding to such events as selection changes in Microsoft Word or new mail items in Microsoft Outlook.
The most common, versatile way to customize and extend Office 2000 is by developing a Component Object Model (COM) add-in. A COM add-in is a .dll or .exe file that's registered on a user's machine. You can write code in any programming language, such as Visual Basic or Microsoft Visual C++, and use the same add-in code and file in any Office 2000 application. Once you know how to create a COM add-in, you'll be able to create an add-in for any Office 2000 application.
This chapter describes the most common features of add-ins and shows you how to build a COM add-in from start to finish.