Microsoft went to the Open XML Format for its Office documents beginning in 2007. The Open XML format files are smaller than previous file formats. An Excel Workbook 2007 or 2010 business file ...

When I send an XLSX file and and XLSM file to be analyzed, they are both identified as XLSX, because they both are a zip file with a file at xl/workbook.xml. The difference between them is that the ...