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…...contents of these older format spreadsheets? Or is simply detecting...the file format, Aspose.Cells API can also detect the application...