Some people prefer to print it out and read it on paper. But if you prefer to read it as a web document, why not convert the PDF to HTML !? I understand there are so many programming languages to choose from so you need to filter them out somehow, but I do not think filtering by documentation formatting is a good heuristic.
A language whose only documentation is paper or PDF (it's not the case of Mercury) is not a language that's going to thrive in this age. It's probably a waste of time to get involved with it. This is why I use documentation format as heuristic.
