You don't necessarily need Microsoft Excel to work with an .xlsx file Reviewed by Ryan Perian This article explains what XLSX ...

If Microsoft Excel fails to recognize a file in the XLSX or XLS format, the data contained in ... Click "OK" to save your changes. Click "Open" on the File tab and then navigate to the folder ...

Image: Microsoft The demonstration .xlsx file contains only one sheet because that’s all the .csv feature supports. Excel won’t allow you to save a multiple-sheet workbook to .csv format.