"Only old PDFs have this problem." Fact: Modern PDFs created from web browsers (printing a webpage to PDF) frequently lack font embedding.
This is a notorious issue for business presenters. You might design a stunning presentation on your home Mac using a sleek, platform-specific font. When you copy the file to a flash drive and open it on a corporate Windows machine at a conference, PowerPoint will substitute the font, often breaking text alignments and layouts. 3. Print Drivers and PDF Generation Download Font Substitution Will Occur