stands for Character Identifier . These are used in Adobe PostScript and PDF files to manage large character sets, particularly Asian languages (Chinese, Japanese, Korean) or complex symbolic fonts.When a PDF is generated, if the software does not properly embed the original font (due to licensing restrictions, corruption, or technical errors), it creates a temporary, generic placeholder font named something like CIDFont+F1 or CIDFont+F1+Bold . 2. What Do F1-F5 Represent?