SLDocument sl = new SLDocument("example.xlsx", "Sheet1");
        int rowNum = Convert.ToInt32(barcodeNum.Text);
        string cellAddr = "C" + barcodeNum.Text; 
        string cellEnvelope = "B" + barcodeNum.Text;
        string cellOutDate = "E" + barcodeNum.Text;
        int envelopeNumber = Convert.ToInt32(envelopeNum.Text);
        string address = sl.GetCellValueAsString(cellAddr);
        MessageBox.Show(address);
        sl.SetCellValue(cellEnvelope, envelopeNum.Text);
        sl.SetCellValue(cellOutDate, DateTime.Now);
        sl.SaveAs("Example.xls");