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 format was developed to simplify use of Type1-fonts in some software. It’s 8-bit and so it’s quickly processed by programs and it has a compact structure. PFB contains additional metadata. Besides the storage of system fonts, a good example of its use is its application in AutoCAD to create font files with compilation.