Not something I have used, but you can check and see if checking the ready
property of the application object will indicate this:
Sub UseReady()
If Application.Ready = True Then
MsgBox "Application is ready."
Else
MsgBox "Application is not ready."
End If
End Sub
However in one thread someone said it returned true regardless of the state
of edit mode. The Ready property is in xl2002 and later. \
this is vba code to check the state of the Open menu item if you want to try
and to it in C#.
Dim C As Office.CommandBarControl
Set C = Application.CommandBars.FindControl(ID:=23) ' Open
button
If C.Enabled = True Then
Debug.Print Now, "Not Edit Mode"
Else
Debug.Print Now, "Edit Mode"
End If