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 was developed by the Adobe Company and contains data regarding the metric characteristics of Type 1 PostScript fonts. The AFM structure requires a control template that defines the look of every font symbol. It’s used primarily for UNIX.