Excel File Extensions and Their Uses
XLS vs. XLSX The current default file extension for an Excel file is XLSX. Prior to Excel 2007, the default file extension was XLS. Determine if a file contains macros before you open it. Macros contain code that could damage files and compromise computer security if they come from untrusted sources. Excel files containing VBA and XLM macros use the XLSM extension. XML and HTML XML stands for extensible markup language....