As much as I detest most formats, etc from the propietary world, I'm impressed at the utility and longevity of PDFs.
When I want a true interoperable WISYWIG, that's read-only, there's no comparison (as embarrassing as it is to admit).
Discussion
Making the PDF reader universally free, and licensing it other devs so their formats can be easily converted had a lot to do with its ubiquity, and longterm success.
Yeah.
It uses binary to display plain-text, and has to be interpreted by PostScript, but end users just see the resulting image and don't realize the technical bloat on top.