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.

If the Sorry, Excel cannot open two workbooks with the same name at the same time error is preventing you from using Excel, see this post.

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 ...

Numbers has the ability to open Excel files so you can work on them. You can also export spreadsheets in Numbers so that they are compatible with Excel.

Has someone sent you a .numbers file that you can't open in Excel on your Windows PC? Here's how to edit it using Apple's iCloud apps ...