private void MostrarPDF(object sender, RoutedEventArgs e)
 {
     try
     {
         FacturaElectronicaPDF pdf = new FacturaElectronicaPDF();
         pdf.MostrarFactura(pdf.CrearFactura(fac));
     }
     catch (Exception ex)
     {
         this.LogError(ex);
     }
 }