If you cannot open an Excel file and see Excel cannot open the file because the file format or extension is not valid error, see this post.

On the right side, select the Open checkboxes for the file types that you want to open in the Protected View. Now, select the Open selected file types in Protected View radio button at the bottom.

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 ...

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 ...

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 ...

Go to the File Types tab, scroll down to Microsoft Excel Worksheet (.xls not .csv) and click Advanced. Uncheck 'Browse in same window' (or 'Open Web documents' in place) and OK.