XLS files are Excel workbook files created in Excel 97 or Excel 2003. The 2007, 2010 and 2013 versions of the program use the XLSX format by default to save workbooks, but can also use the XLS format.

Ankush khandelwal asked about compatibility issues between files created in different versions of Microsoft Office–specifically the big changes in file format that came with Office 2007. With Office ...