Public ReadOnly Property UndoManager As UndoManager

public UndoManager UndoManager {get;}

private void mnuEditUndo_Click(object sender, System.EventArgs e)
{
    this.ardMain.UndoManager.Undo();
}

'mnuEditUndo_Click - calls the UndoManager.Undo command from the Designer
Private Sub mnuEditUndo_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles mnuEditUndo.Click
    Me.ardMain.UndoManager.Undo()
End Sub 'mnuEditUndo_Click