Conversion of bak files to xls file format

It is only possible to convert .bak files as excel spreadsheets (.xls) if these backups actually contain some kind of table, spreadsheet or database in first place. Some programs just simply rename the extension from original to bak, so no bak to xls conversion is needed, just rename the file back (in this case .xls)  If this doesn't work, then you probably have no way how to reliably convert the data, because bak is too much of a generic file extension and you would need a special file identifier to determine what file type it actually is.

Open BAK file    Open XLS file