Practically all papers published at CEUR-WS.org are published in the PDF format. This is now a quite old format, originally developed for printing. I still regard it as a good paper format, in particular when the PDF file is supporting navigation and easy lookup of references.
However, it is not a format that allows easy searching/querying of papers because it has no meaningful semantic annotation of its contents.
There are a few papers in CEUR-WS that were actually written in a semantically enriched HTML format. Will such a format become more popular for academic publishing? Or are we stuck with PDF for the foreseeable future?
I personally believe that papers should also be data, i.e. it should be possible to query the contents of a paper. There are initiatives like the open knowledge graph at TiB Hannover to represent the research questions, methods and results in a way to facilitate semantic queries across a large collection of papers. I find that very promising but apparently PDF does not support such machine-readable content at all.