[dragonwriter]

PDF a perfectly portable in the digital world (the only world in which it has ever existed.)

It's not perfectly optimized for every display (or print page, the two being equivalent) size, resolution, etc., but then neither is any other format that can handle the same range of content, nor will any format ever be until we have AI layout that does as good as professional layout from a single source file for all media sizes and properties.

I find professionally laid out PDFs that are designed for letter/A4 size pages to superior in practical use to any reflowable format I've yet seen at pretty much every size for most content more complex than plain linear text like you'd find in a novel. (Smartphone and smaller devices aren't great for it, but then they aren't great for reading content more complex than linear text regardless of format.)