You cannot write programs in PDF. As I have written, it is not a programming language. It is already interpreted. For your use-case a PostScript file is better,

You cannot write programs in PDF. As I have written, it is not a programming language. It is already interpreted. For your use-case a PostScript file is better, that's why you used it. But most of the time all graphics for a given page are prerendered and therefore static. If all page content is vector based you can render a PDF in every resolution you need. In my little printing world I like to have control over the page, I don't like that the printer (RIP) can control the page "in a way that is optimal for the printer". I am responsible for the output, not the printer. If something goes wrong inside the RIP, the printer doesn't pay the damages, I am. And things can get costly. It is also pretty resource intensive to work with PS (because it has to be interpreted every time you want to have a look at it). All things considered (and there are a lot more differences) it is simply more pleasant to work with PDF instead of PS. That's why the majority uses it. But it definitely has flaws, too.