When you try to open an Excel file, make sure the file’s icon matches the file type. If it doesn’t, enable the File name extension option in File Explorer and check the extension of the file.

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 workbooks, but can also use the XLS format.

Try renaming the file with the correct extension (e.g., .xlsx for Excel workbooks). If needed, open the file in Excel, save it as the correct format, and close it to apply changes.