public void PopulateData(int invoiceID)
 {
     rsInvoiceHead             = SalesOrder.GetInvoiceHead(invoiceID);
     rsInvoiceDetail           = SalesOrder.GetInvoiceDetail(invoiceID);
     lblConfirmation.Visible   = false;
     btnConfirmInvoice.Visible = false;
     btnGeneratePDF.Visible    = true;
     PopulateData();
 }