Private Sub btnBold_CheckedChanged(ByVal sender As Object, ByVal e As _
  System.EventArgs) Handles btnBold.CheckedChanged
            rtbText.SelectionFont = New Font(rtbText.SelectionFont.FontFamily, _
                                             rtbText.SelectionFont.Size, _
                                             rtbText.SelectionFont.Style Xor _
                                             FontStyle.Bold, _
                                             rtbText.SelectionFont.Unit)
 
End Sub