The person who created the PDF did not embed the fonts into the file. The document expects your PDF reader to provide them.
Be cautious of websites claiming to offer "Cid Font F1 Free Download." Because these are internal PDF labels and not real retail fonts, such downloads are often or generic font files renamed to match your search query. CID+ Fonts - Adobe Community Cid Font F1 F2 F3 F4 Free Download
If you need to replace these missing placeholders with functional fonts, reputable libraries offer broad language support that can often mimic the original intended look: The person who created the PDF did not