You likely encountered this while opening a PDF or AI file and received a "Missing Font" error. This happens because: CIDFont+F1 issue - Adobe Community
In a standard CJK CIDFont, the /CIDSystemInfo dictionary contains: cidfont f1 normal fixed
: When software exports a PDF and cannot fully decode or embed the original font names, it assigns aliases like F1, F2, or F3 to track different styles or weights used in the document. Fixed/Normal Attributes You likely encountered this while opening a PDF