Word 2007 uses Office Open XML (DOCX) as its default format, but retains the older binary format for compatibility reasons. Office Open XML used in Word 2007 is not identical to approved ISO/IEC 29500:2008 Office Open XML because of changes in format specification during standardization process. Microsoft has declared that Office Open XML is already partially supported in Office 2007, but the company plans to update that support to full ISO standard in the next major version release of the Microsoft Office system, named "Microsoft Office 2010".
Microsoft has published specifications for the Word 97-2007 Binary File Format and the Office Open XML format. Microsoft has moved towards an XML-based file format for their Office applications with Office 2007: Office Open XML. This format does not conform fully to standard XML