Click-bait title. It's about devices, not the actual digitized book. I have .pdf files from 90's when I started to learn assembler, they still apply (for basic and medium) today and I can read them just fine on my Foxit reader.
to be fair there are books from hundreds of years ago written in dead languages which you can't read anymore easily.
as for file formats, pretty sure you can find readers in some internet archive + operating systems which you can just as easily get/create and emulator for.
