If you are looking for "Cid Font F1 F2 F3 F4 F5," you likely encountered these names as "missing font" errors while opening a PDF in software like Adobe Illustrator or Affinity Designer.
F2 — Cid F2 (Text Serif)
used in your PDF so you can find the correct legitimate font to download? CIDFont+F1 issue - Adobe Community Cid Font F1 F2 F3 F4 F5 Free Download