This is a format for presenting fonts in PDF files that was initially conceived to store symbols in the Japanese and Chinese languages because it had a 16-bit structure and allowed for more precise adjustment. CID expands the the potential for PostScript by supporting languages that do not have a left-to-right orientation, and by supporting even a vertical mode of orientation.
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.