IANAP but it's kind of fun to try to read the start of the PDF, it doesn't seem to require much advanced math. But information is not abstract in the same sens

IANAP but it's kind of fun to try to read the start of the PDF, it doesn't seem to require much advanced math. But information is not abstract in the same sense as, say, the set of all prime numbers, for it only exists when it is physically instantiated. This seems to be an important point to Deutsch, but it doesn't seem completely obvious to me. E.g. I can reason about the effects of purely hypothetical information which in fact does not exist.