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.

If you use Microsoft Excel on your Mac, you can save the spreadsheets you create and open them in Numbers, Apple’s spreadsheet app. It’s a handy feature to use in case you can’t access Microsoft’s ...