You’ll find them in , PDF 1.2+ , and macOS system fonts.
To keep file sizes small, software often only embeds a "subset" (just the characters used in that specific document). If the PDF gets corrupted, the reader loses the map to those characters. cid font f1 f2 f3 f4 f5 f6 f7 fonts free download link
This is often the simplest solution. The built-in Preview app in macOS can sometimes successfully re-interpret fonts that Adobe Acrobat Reader fails to recognize. You’ll find them in , PDF 1
Because these names are just generic labels (aliases), there is no official "CIDFont F1" file to download. You’ll find them in
Understanding CID Fonts: Fix Missing F1 to F7 Fonts and PDF View Errors