.DFONT File Extension
What is a DFONT file?
Standard font format used by Mac OS X; font contents are stored in the data fork part of the file instead of the resource fork (which was used by fonts in Mac OS Classic).
Active system fonts (which can be accessed by all users) must be stored in the /Library/Fonts/ folder. Active user fonts (which can only be accessed by the current user) must be stored in /Users/~username/Library/Fonts/ folder.
DFONT files can be opened by Font Book, or by other Mac OS X programs that access system fonts.