12. The VSTO Programming Model
The VSTO Programming Model for Documents
In Windows Forms programming, a form is a window that contains controls, such as buttons, combo boxes, and so on. To implement a form, you can drag and drop controls from the Visual Studio toolbox onto the form’s designer. The form designer then generates a customized subclass of the Form class. Because each form is implemented by its own class, you can then further customize the form code by adding properties and methods of your own to the class. And because all the controls are added as properties on the form class, you can use IntelliSense to more rapidly program those custom methods.
VSTO’s system of host items and host controls is directly analogous to Windows Forms. ...