When a user drags a tool from the Tool Palettes window, the framework queries the tool's stock tool object for the IAcadToolDragSource interface. If an implementation of this interface is found, the framework calls its BeginDrag(), DragInProgress(), and EndDrag() methods to allow the tool application to prepare for and clean up after the drag operation.
If a tool is dropped in the AutoCAD drawing editor, the framework calls the DragEnterDrawing(), DragOverDrawing(), DropInDrawing(), and DragLeaveDrawing() methods from its IAcadToolDragSource object. Your application should implement these methods if you want to control what happens during these events. If you have not implemented DropInDrawing(), the framework simply executes the tool.