If you are working on a specific PDF with f1…f6 and need to reduce or analyze them, tools like cpdf (Coherent PDF), hexaPDF (Ruby), or pymupdf (Python) give programmatic control.
Editing a PDF with multiple CIDFont subsets causes missing characters. Cause: Adding text not present in any existing subset ( +f1 .. +f6 ). Fix: Subset the missing glyphs into a new subset ( +f7 ), or embed full font. cidfont+f1 f2 f3 f4 f5 f6
Would you like a Python script example that iterates through all CIDFont subsets in a PDF and reports their original font names and glyph counts? If you are working on a specific PDF
qpdf --qdf --object-streams=disable document.pdf unpacked.pdf grep -A5 "/CIDFont" unpacked.pdf You will see something like: qpdf --qdf --object-streams=disable document
This is an excellent and highly technical topic. The notation cidfont+f1 , cidfont+f2 , etc., is specific to and PDF internals, usually observed in PDF stream dumps , PostScript printer logs , or extracted font debugging output .