: PDFs that combine various global scripts.
The suffixes (and sometimes beyond) are arbitrary internal names assigned during the PDF generation process. In many cases, these numbers correspond to different weights or styles of the same font family used in the document: Impossible fonts to be found / Fontes impossíveis de achar cid font f1 f2 f3 f4
: Modern OpenType fonts often get converted into CID encoding when they are embedded into a PDF to ensure all characters display correctly. Decoding "F1, F2, F3, F4" : PDFs that combine various global scripts
: Chinese, Japanese, and Korean writing systems. F4" : Chinese