convert from xls to xlsx C#
/// <summary>/// Using Microsoft.Office.Interop to convert XLS to XLSX format, to work with EPPlus library/// </summary>/// <param name="filesFolder"></param>
public static string ConvertXLS_XLSX(FileInfo file)
{
var app = new Microsoft.Office.Interop.Excel.Application();
var xlsFile = file.FullName;
var wb = app.Workbooks.Open(xlsFile);
var xlsxFile = xlsFile + "x";
wb.SaveAs(Filename: xlsxFile, FileFormat: Microsoft.Office.Interop.Excel.XlFileFormat.xlOpenXMLWorkbook);
wb.Close();
app.Quit();
return xlsxFile;
}