This was created for the Mac OS X operating system. Unlike the old operating environment versions, the font is stored in the thread of a data file instead of in resource threads. It’s been used as a container for TrueType fonts since 2009 after the release of Mac OS X 10.6, and is gradually replacing the TrueType Collection.
This is a format for storing raster and vector fonts created or changed in FontForge. By opening an SFD file in this program you can store it in any modern font format like TrueType or OpenType. SFD contains all the information about the point setting of each symbol created or changed in FontForge.