Compatibility Mode is used when you open a document created in an older version of Microsoft Word, like Word 2007 or Word 2010. When this happens, the document appears in Compatibility Mode.

In this mode, some features are disabled. You can only use commands that were available in the version the document was made with. For example, if you open a Word 2007 document, you will only see the options that were in Word 2007.

To exit Compatibility Mode, you need to convert the document to the current Word version. However, if you're working with others who use an older version, it's best to keep the document in Compatibility Mode to avoid changing the format.

To convert the document, go to the File tab and click "Convert". 

Then, confirm the change by clicking OK. After converting, the document will be updated to the current version, but this may cause some layout changes.