CIDFont (Character Identifier Font) is a specialized way of encoding font data to support complex character sets, particularly for Asian (CJK) languages. When a PDF is created using software like Adobe InDesign, it may embed a subset of an existing font—like or Myriad Pro —and rename it to a generic placeholder like CIDFont+F1 or CIDFont+F2 .

and then using "Export as PDF" often flattens the file and makes the text readable again. Transparency Flattener:

Is the text in a like Japanese or Chinese?

: A popular resource for a wide variety of creative and experimental styles. alternative fonts that match a specific design style or need help fixing a specific PDF CIDFont+F1 issue - Adobe Community