This type allows users to extend various context (shortcut) menus in AutoCAD. There are 3 scenarios where this class can be used: 

• Extending the default context (shortcut) menu. (See Application.AddDefaultContextMenuExtension>.)
• Extending the object context (shortcut) menu. (See Application.AddObjectContextMenuExtension>.)
• Extending the command context (shortcut) menu. (See CommandMethod.ContextMenuExtension>.)

Autodesk.AutoCAD.Windows.Menu
    Autodesk.AutoCAD.Windows.ContextMenuExtension

Public Class ContextMenuExtension
Inherits Menu
Inherits IDisposable

public class ContextMenuExtension : Menu, IDisposable;