How to copy the XLSX file to XLS file using C#

You can pen the xlsx file programmatically using excel interop and save it as xls file.

Excel.Application oXls = new Microsoft.Office.Interop.Excel.ApplicationClass();
                    
object oMissing = System.Reflection.Missing.Value;

                   
                   Excel.Workbook oSpr = oXls.Workbooks.Open("ExcelData.xlsx", oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing);
                   object fileFormat = Excel.XlFileFormat.xlXMLSpreadsheet;
                
                   
                    oSpr.SaveAs("ExcelData.xls", ref fileFormat, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing);
                    oSpr.Close();
                    oXls.Quit();

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