: In some cases, these identifiers define different weights of the same typeface. For example, F1 might be Arial Bold, while F2 is Arial Regular.
Sometimes, a PDF creator only embeds a subset of the CID font (only the characters used in the document). If you edit the text and type a new character not in the subset, the reader looks for it under the F1 tag, finds it missing, and substitutes a random garbage glyph. Solution: When exporting from Illustrator or InDesign, check "Embed Entire Font" (warning: this increases file size significantly). cid font f1 f2 f3 f4
When you embed a CID font in a PDF, the subset might be labeled internally as F1+ , F2+ , etc. If a PDF processor cannot read the original CMap, it may fall back to these generic F1-F4 placeholders. : In some cases, these identifiers define different
CID+ Fonts - Adobe Community