After the MS16-088 patch is applied, though, Excel refuses to open XLS files, showing a blank screen instead of a workbook. Poster conker123 on the TechNet Office forum described the problem ...

If you see The file couldn't open in protected view error while opening Microsoft Excel, the fixes listed in this post will help you.

If Excel Online is not working and you see errors Couldn't Open the Workbook, or Request Was Taking Too Long, then see this post for the fix.

While it is technically possible to open an Excel file in Notepad, this is not a good idea. Excel files are binary files that contain complex formatting and data structures. When you open an Excel ...

How to open a .csv file in Excel Opening a .csv file is as easy as opening a .txt file, and usually, you won’t have to clean up the data before doing so because the save task inserts the delimiter.

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.

This suite’s Excel counterpart, Calc, should open a corrupted Excel file. Unfortunately, it means a lengthy download, but if it works, it’s well worth the effort.