I am pretty sure the answer is: you can't. UltraTextEditor does not handle that message as native .NET controls only handle windows messages by necessity, since doing so constitutes unmanaged code, which we try to avoid when possible.

UltraTextEditor uses a TextBox control to realize the editing, and you can override the WndProc for a TextBox, but in this case you have no chance to intercept the instance we create, so you can't override that method.

If you describe in detail the reason you want to do this, we might be able to come up with an alternative solution.

I'm not sure what you are asking. But my guess is that the UltraTextEditor will probably never get this message. When UltraTextEditor goes into edit mode, it displays another control on top of itself which derives from TextBox. So if the control is in edit mode, any windows messages will go to the embedded TextBox control and you will not be able to get to those message, since you cannot override the TextBox control.