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.

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 ...

There are a couple of ways to have Excel open most conveniently for you.

Click "File," "Open" and browse to your second Excel file. Double-click the file to open it. Repeat the steps for each new file you'd like to open in its own window.

Microsoft Word can accommodate a surprising number of file formats, and even take in Excel and PowerPoint data, though it might look funny. Here's how.