: If you are on a Mac, open the PDF in the Preview app and select File > Export as PDF . This often flattens the file and replaces the broken placeholders with readable text.
sudo updmap-sys --enable Map cid.map
If the specific fonts (f1-f6) are proprietary or unavailable, you can map them to a system-installed font in the cidfmap file to prevent the error: cidfont f1 f2 f3 f4 f5 f6 install
However, PDFs also use generic placeholder names for CIDFonts when the original font cannot be embedded or identified. That’s where come in. : If you are on a Mac, open