1-) C# RMOS - excel xls to xlsx excel to repair excel repair

// Install-Package Microsoft.Office.Interop.Excel -Version 15.0.4795.1000

 string sourceFilePath = @"C:\SQL\b.xls";

            string savedFile = @"C:\SQL\b2.xlsx";

            Missing missing = Missing.Value;

            Microsoft.Office.Interop.Excel.Application excel = new Microsoft.Office.Interop.Excel.Application();

            Workbook workbook = excel.Workbooks.Open(sourceFilePath,

                missing, missing, missing, missing, missing,

                missing, missing, missing, missing, missing,

                missing, missing, missing, XlCorruptLoad.xlRepairFile);

            workbook.SaveAs(savedFile, XlFileFormat.xlWorkbookDefault,

                missing, missing, missing, missing,

                XlSaveAsAccessMode.xlExclusive, missing,

                missing, missing, missing, missing);

            workbook.Close(true, missing, missing);

2-) bakmasanda olur gibi

Install-Package FreeSpire.XLS -Version 9.2.1

 Workbook workbook = new Workbook();// Install-Package FreeSpire.XLS -Version 9.2.1

 workbook.LoadFromFile(e.FullPath);// a.xls

 workbook.SaveToFile(e.FullPath+"x", ExcelVersion.Version2013);// a.xlsx