The EN_DROPFILE notification message notifies a rich edit control’s parent window that the user is attempting to drop files into the control. A rich edit control sends this notification message in the form of a WM_NOTIFY message when it receives the WM_DROPFILES message.
EN_DROPFILES wParam = (WPARAM) (UINT) uID; lParam = (LPARAM) (ENDROPFILES FAR *) lpEnDropFiles;
Returns a nonzero value to allow the drop operation or zero to ignore the drop.
For a rich edit control to receive WM_DROPFILES messages, the parent window must register the control as a drop target by using the DragAcceptFiles function. The control does not register itself.