When a new version of Microsoft Word is released, it has the ability to save "down" to previous versions, since not every user upgrades to the latest version at the same time. This backward saving allows users with differing versions to continue to work together. In the past, saving backwards sometimes caused unpredictable results if the newer version of the software had features the earlier version couldn't understand. Word compatibility mode allows the user to turn off new features that may not be recognized by earlier versions so the document remains fully compatible with earlier versions of Word.
Word compatibility mode was incorporated first into Word 2007 for Windows and Word 2008 for Macintosh. Both these versions of Microsoft Word now incorporate the new Office Open XML format, indicated by the file extension .DOCX instead of the old .DOC extension earlier versions of Word used. This XML format, however, is not fully backwards compatible with earlier versions of Word, so a special compatibility mode was added to new versions of Word to allow users with different versions of Word to continue to share documents.
Word compatibility mode makes sharing documents with other Word users easier by enabling the user to restrict features used in the document that aren't recognized by earlier versions of Word. Since there are at least five older versions of Word that still work on current Windows and Mac operating systems, and because it usually takes a while for everyone to upgrade to a new version of software, there's always a possibility that someone a user shares documents with will need files sent in .DOC format instead of .DOCX.
Word compatibility mode recognizes documents from earlier versions of Word and saves the file with the .DOC extension so earlier versions of Word, as well as the new version, can continue to read it. Any document with the .DOC extension opened in Word 2007 or 2008 is automatically opened into Word compatibility mode to prevent the user accidentally adding advanced features an earlier version of Word won't understand. Turning off compatibility mode is easy to do using the Save As command to save the document with the .DOCX extension.
Items That Change in Compatibility Mode
When a document is opened in compatibility mode, the title bar of the document reflects the mode status. In compatibility mode, Office Art diagrams are converted to images and are no longer editable. Also, SmartArt Graphics cannot be added to a document in compatibility mode. Other Word 2007/2008 features change as well. Fonts, for example, used as part of themes will revert to standard formatting and changing themes will no longer update them; any themes uses in a .DOCX file will be converted to styles since themes is a new feature introduced in Word 2007/2008. Text boxes created with relative positioning will be converted to absolute positioning, and bibliography and citation information will no longer update automatically.
When saving a document, a compatibility check can be done in the Save As dialog box. This reports which versions of Word are best able to read the document and notes any areas of the document likely to cause problems in another version of Word. On an individual document basis, the user can set compatibility preferences to ensure that the document remains backward compatible with a particular earlier version of Word while working on it. The ranges of compatibility are divided into 2000-2004 and X, 97-98, and Word 6.0/95. Even earlier versions are still possible too: Word for WIndows 1.0/2.0, Word for Mac 5.x, Word for DOS, and older versions of Word Perfect, 5.x-6.x.