I mean there’s no layout engine to do things like wrapping and line height etc. Everything is explicitly positioned.

PDF seems a bit more bonkers because you render text as strings of glyphs and the conversion back to text is an afterthought. There’s a ToUnicode map that says “glyph 8 in the embedded font is an ‘X’” but that’s there for copy pasting / searching - not for rendering. PDFs are built to render glyphs at positions.

Edit: to go full meta, there are Type3 fonts where each glyph itself is defined as a PDF graphics stream. Which actually leads you in to what’s inside a font. Guess what? lots of them look just like PDFs inside, because the glyphs are defined in postscript. Fonts are PDFs kinda grew up together, and once you start digging into them the similarities are striking.

Yeah it's definitely a presentation format, but probably the most useful one there is for many. As someone who does print design, screen design, and development work, I'm glad PDF is what it is. Absolute subpixel-level perfection, support for raster and vector visuals, embedded fonts, multiple industrial color encoding formats, and other professional design features are essential for designers. Adding generalized formatting rules for dynamic layouts and content would needlessly complicate an already useful tool to adress use cases satisfied in other formats. That people, Adobe included, use it as a general document format is a problem with usage and product management, not the format. It pisses me off when it's used as the default export format unless it's sole purpose is for printing. I've had to write web apps that dynamically generated pdfs: it was a pretty miserable pierces that yielded mostly lackluster results. Glad to see Adobe has moved away from their cockamamie pdf interactive features that contributed little more to users than anxiety about security holes.

Epub should be the defacto standard when the included data remains important.