[joeyrobert]

UCI chess engines typically defer opening book to the GUI consuming it. So if you were using Stockfish with Arena or Tarrasch, that would handle the opening book. Stockfish will start calculating when it is out of the book. This is all configurable, of course.

[Philomath]

I had no idea openings were so fixed from the computers point of view. Does this mean that in order to become a better player it is a must to learn all the openings as a book?

[PikelEmi]

Up to an ELO rating at 2000 (and even beyond that) there is no need to memorize openings. It is much more important to learn the basic opening and development ideas. Even if you play against non-masters who have memorized some openings you can easily crunch them by the basic ideas. It takes master level to go from memorize to actually understand how a given opening works.

[TylerE]

Really if your're good enough...

Magnus Carlsen spends very very little time on memorizing openings.

[govg]

Even in professional chess, openings are almost "by the book". There are quite a few main lines of openings and play is almost always along one of them, or variants thereof.