How to Open an XLS File in Excel. 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 ...

This change means that files saved from Excel 2007 or later won't open natively in Excel 2003 or earlier.

You don't necessarily need Microsoft Excel to work with an .xlsx file This article explains what XLSX files are, how to open them, and which programs are able to convert them to other spreadsheet ...