Microsoft Office: Compatibility Mode
Compatibility Mode is a feature in Office 2013, 2010, and 2007 that allows you to open and edit older Office documents such as .doc, .ppt, and .xls files. Opening any of these types of documents in an Office 2013, 2010, or 2007 application will activate the Compatibility Mode automatically. If you make changes to your old document and save them, the document will save as the old format.
If you are viewing a document in Compatibility Mode, you can easily convert the document to 2013, 2010, or 2007 (.docx) so that you can use the newest features that those versions offer.
However, when you use these new features/convert a document to 2013, 2010, or 2007, users who try to open the file in older versions (Office 93-2003) will not be able to use all of the new features. To make the document fully readable in older versions of Office, you must save the 2013/2010/2007 file in Compatibility Mode.
Office 2007 and 2010 use the same document formats (i.e., .docx, .xlsx, .pptx). If you open a 2007 file in 2010, Compatibility Mode will activate. If you open a 2013 file in 2010, you may receive an error telling you that some features are not available if the file was created with 2013 only features.