Checks if the subset fonts embedded in the document (if any) contain a complete character or CID set.
If a font is subsetted, only the characters of the font that are actually used in the text are embedded in the document. This is done to to keep a file as small as possible. This Action allows you to check if all characters of the font are embedded. In case of simple fonts, the complete set is referred to as "CharSet"; in case of composite fonts, it's referred to as "CIDSet".
CID (Character Identifier) fonts are a format of Type 1 fonts that are typically used for Chinese, Japanese and Korean fonts.