What is a Default XLS File Name?
Workbook1.xls - The default file name that Microsoft Excel gives to new spreadsheets before Excel 2007, creating new spreadsheets with the filename Workbook1.xlsx.
How to Open XLS File?
You can open XLS files with Microsoft Excel in Windows and in macOS. Excel is the best program for opening XLS files because it fully supports the formatting of Excel spreadsheets, which includes data fields and graphs. Excel is also available for Android and iOS devices. There are a large number of other spreadsheet programs that can open and edit XLS files but they may not fully support the formatting of the XLS spreadsheets. Alternative programs include Corel Quattro Pro (Windows), Apple Numbers (Mac), and OpenOffice Calc (multiplatform).
You can also open XLS files with various web programs. Google Sheets is a great free option that allows you to upload an XLS file and view, edit, save, and convert the spreadsheet.