You can also open and edit XLSX files without Excel, completely free, using WPS Office Spreadsheets, OpenOffice Calc, or LibreOffice Calc. If you're on a Mac, Apple Numbers supports XLSX files ...

How to Open Excel 2007 Files As Separate Windows. If you work with multiple Excel files over the course of a workday, and especially if you use a dual-monitor setup, you might wonder how you can ...

Likewise, the venerable .xls Excel spreadsheet format gave way to .xlsx, and PowerPoint .ppt files became .pptx files.