It is true that Word does not expose any events that fire when the user
moves the cursor by typing but ...

... the WindowSelectionChange Event does fire when the user moves the
cursor with the arrow keys or clicks somewhere with the mouse so that can
catch a lot - probably everything you want to.

Try something like this:

Private Sub wd_WindowSelectionChange(ByVal Sel As Selection)

   Dim UserPos As Range
   Dim EditablePos As Range
   Set UserPos = Selection.Range.Duplicate
   Set EditablePos = UserPos.GoToEditableRange
   If UserPos.Start > EditablePos.End Then
       ' tried to select past last range - just go to beginning of it
       UserPos.Start = EditablePos.Start
       UserPos.End = EditablePos.Start
   Else
       ' If selection starts before an editable range move the start to the
start of that range
       ' If the end is also before the start move end to the start as well
       ' If the end is after the end of the editable range pull it back in,
else leave it alone
       If UserPos.Start < EditablePos.Start Then
           UserPos.Start = EditablePos.Start
           If UserPos.End < EditablePos.Start Then
               UserPos.End = EditablePos.Start
           ElseIf UserPos.End > EditablePos.End Then
               UserPos.End = EditablePos.End
           Else
           End If
       Else
           ' Selection already starts in an editable range - leave it alone
           ' If the end is after the end of the editable range pull it back
in, else leave it alone
           If UserPos.End > EditablePos.End Then
               UserPos.End = EditablePos.End
           End If
       End If
   End If
   ' Select the amended range
   UserPos.Select

End Sub