Use mutool info (from MuPDF) or pdf-parser.py:
mutool info broken.pdf | grep -i cidfont
If you generate PDFs programmatically (iText, Prawn, PyPDF2, or Apache PDFBox), here is how to avoid creating broken CIDFontF1–F6 references. cidfontf1 f2 f3 f4 f5 f6 updated
The keyword "updated" signals significant changes in the PDF specification (ISO 32000-2:2020 also known as PDF 2.0) and how modern software handles older CIDFonts. Use mutool info (from MuPDF) or pdf-parser
Here are the key updates as of recent years: If you generate PDFs programmatically (iText, Prawn, PyPDF2,