[mananaysiempre]

This might actually be causal to an extent. A sibling comment mentions the early-mover advantage they got for their software from originating the format (initially in a locked-down form—IIRC, they actually prohibited Microsoft from including a PDF export feature in Office in the 90s). But another contribution to this is that there’ve put an absolutely unbelievable amount of stuff into the format while they were still milking it (how many flavours of PDF forms are there? three I think, one of which is XForms submitted over something equally execrable? also JavaScript support of course, can’t forget about the JavaScript support); and Acrobat is the only piece of software that supports—has to support—them all.