The format type .XLSM is an Excel XML workbook first introduced with Excel 2007 that can store VBA macro code. XML (Extensible Markup Language) is a text format for documents that define structured data. You may need to convert XLSM to XLS if you need to be able to open a file in a version of Excel older than 2007.
Open the 2007 version of Excel or later. Click "Open" in the "File" drop-down menu. Open the .XLSM file from the folder tree that opens up.
Click "Save As…" in the "File" drop-down menu. Select "Excel Workbook" as the format. Check the portability notes of the format at the bottom of the Save panel to confirm the format has adequate backward portability for your needs.
Convert the XLSM file using an older version of Excel the same way by first downloading the converter titled "Microsoft Office Compatibility Pack for 2007 Office Word, Excel and PowerPoint File Formats." Before downloading the converter, it is important that you update your version of Microsoft Office to the latest service pack (see Resources).