Document.UndoClear Method ()
Clears the list of actions that can be undone for the document. Corresponds to the list of items that appears when you click the arrow beside the Undo button on the Quick Access Toolbar.
Assembly: Microsoft.Office.Tools.Word (in Microsoft.Office.Tools.Word.dll)
Include this method after a method in your code to keep Word object model actions from appearing in the Undo box.