private void cboalineacion_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (cboalineacion.SelectedItem == "Izquierda")
        {

            rtxTexto.SelectionAlignment = HorizontalAlignment.Left;
        }
        if (cboalineacion.SelectedItem == "Centrado")
        {

            rtxTexto.SelectionAlignment = HorizontalAlignment.Center;
        }
        if (cboalineacion.SelectedItem == "Derecha")
        {

            rtxTexto.SelectionAlignment = HorizontalAlignment.Right;
        }


    }