Traditional PostScript fonts (Type 1) and TrueType fonts were designed for Western languages. They use an 8-bit encoding system, meaning they can only support 256 characters per font. This works perfectly for English, French, or German, but fails catastrophically for languages like Japanese, Chinese, and Korean (CJK), which contain thousands of unique characters.

is simply the fourth unique CID font. In complex, multi-language documents (e.g., a technical manual in English, Japanese, Korean, and Traditional Chinese), you might use F1 through F4 (or even F5 and beyond, though F1–F4 are the most commonly referenced in legacy hardware).

If you receive a file and see an error saying "CIDFont+F1 cannot be created," it means your system cannot find the original typeface or the necessary mapping to display the characters.

The software assigns "F1," "F2," etc., as generic IDs for the different font styles it found in the document.

Adobe introduced the format in the early 1990s to solve this problem. Instead of limiting itself to 256 glyphs, a CID font uses a 16-bit (or 32-bit) space, allowing for up to 65,535 characters. This is achieved through a two-part structure:

or various PDF creators often assign these arbitrary names (F1 through F4) to fonts it cannot fully encode or name during the export process. Font Subsetting