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.

When you open or create another workbook (an Excel file that can contain one or more worksheets), that opens an internal window within the Excel window.

Open Excel, go to the File menu, click "Open" and locate your file. Hold down the "Shift" key while you click "Open," and continue holding it until the workbook finishes loading.

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.