Often you will open a document in Microsoft Word 2016, and it will display the words [Compatibility Mode] in the title. Each new version of Word introduces an array of new features that were not supported by previous versions of the software. This means that a document that was created by Word 97, for example, will not have been able to take advantage of the new features introduced in Word 2016. When you open this document in Word 2016, then, [Compatibility Mode] is displayed in the title to let you know this.
You can easily convert this document to the Word 2016 format and enable all the Word 2016 features by clicking File > Info > Convert:
After you click the Convert button, you will see the following informational message:
This is purely an informational message, and not something you need to worry about; click OK to continue with the conversion. In essence, the act of conversion will make available all the new Word features, but may also cause some minor layout changes in the document. Converting the document may also reduce its size.
Be aware that converting the document may change its file extension. If you convert a .doc document to Word 2016 format, it will become a .docx document. While you remain in the document, however, its title will still display the .doc extension – but only until you save the document.