Abstruse—usually used in reference to the content of a written, sung, or spoken text—means difficult to understand. Obtuse means (1) not pointed (in reference to an object) or (2) simpleminded or imperceptive (in reference to a person). So, if we go by these definitions, abstruse should never refer to a person or a physical object, and obtuse should never (or very rarely) refer to a text.
The words are often mixed up—for example:
Notoriously obtuse, he is refreshingly straightforward here … [UC Observer]
Likewise, there continues to be no shortage of irritatingly obtuse academic writing floating in the ether and there probably never will be. [Pop Matters]
Mixups like these are so common that we may simply have to accept that the words are variants of each other in some of their definitions. But no doubt careful writers will keep the words separate.
These writers use the words well:
The discourse was too abstruse for the average layman in the audience, but this barely mattered. [BBC]
We can think of several reasons for Harry Reid to resign as Senate Majority Leader, though the flap over his obtuse racial comments isn’t one of them. [Wall Street Journal]
No, not the abstruse stuff of theoretical physics, but the effect of repeated pushes on monetary strings. [Globe and Mail]
Thus, when the green left turn arrow appears, it is set at a sharp angle for St Marks Rd, and at a more obtuse angle for Great South Rd. [New Zealand Herald]