With this method: Dim f As Aspose.Cells.FileFormatInfo = Aspose.Cells.FileFormatUtil.DetectFileFormat("really_old.xls") I am able to detect f.FileFormatType = FileFormatType.Excel95 I realize your product inf…...As "Microsoft Office Excel Workbook". Now you can use Aspose.Cells...2007, 2010, 2013, 2019, 2021 Workbook, Office 365, and OpenOffice...