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

Simply put, .xlsx is a file extension for the open XML spreadsheet used by Microsoft Excel from 2007 onwards. Why the change in format from earlier versions of Excel?

If your Excel files are opening in Notepad on Windows PC, here's how you can reset the settings to make .xls, .xlsx, etc files open in Excel.