The release includes numerous changes, including a new XML-based file format, a redesigned interface, an integrated equation editor and bibliographic management. Additionally, an XML data bag was introduced, accessible via the object model and file format, called Custom XML - this can be used in conjunction with a new feature called Content Controls to implement structured documents. It also has contextual tabs, which are functionality specific only to the object with focus, and many other features like Live Preview (which enables you to view the document without making any permanent changes), Mini Toolbar, Super-tooltips, Quick Access toolbar, SmartArt, etc.
Word 2007 uses a new file format called docx. Word 2000-2003 users on Windows systems can install a free add-on called the "Microsoft Office Compatibility Pack" to be able to open, edit, and save the new Word 2007 files. Alternatively, Word 2007 can save to the old doc format of Word 97-2003.