A while back I ran into an issue where I made a PDF with some text in it, and I could see the text in my PDF viewer, but when I printed it, it disappeared. Eventually I figured out that converting the font to a TTF stopped the problem, but I had no idea WHY that fixed it.

When I found the workaround I posted something like “PDFs are weird” on Mastodon and shockingly someone replied with this incredible deep dive by Leah Neukirchen that explains exactly why this problem happened (even though I didn’t mention ANY specifics about my problem at all): 50 blank pages, or: black-box debugging of PDF rendering in printers