While "CID Font F1" is not a downloadable file, you can often solve the issue by using standard, free, and open-source fonts that comply with CID structures.
are essentially placeholders for the first, second, and third embedded fonts in that PDF document. cid font f1 f2 f3 free download link
The key takeaway is that and expect it to solve the problem. The appropriate solution varies depending on why the placeholder appeared in the first place. While "CID Font F1" is not a downloadable