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.
ICO is a file of this format usually contains a small image icons of different resolutions (16x16, 32x32, 64x64 pixels) and various color depths (16 colors, 32, 64, 128, 256, 16-bit, and so on). Used to display files and folders in the graphical user interface (GUI) operating systems. This format can be opened with the help of the program ACDSee.