Interesting Wikipedia article, but it is very incomplete. (Something I have found is usually the case with any Wikipedia article about SFF.) The "Bootstrap Paradox" only exist in a single timeline universe. In the "Alternate Universe" theory of time travel the "you" coming with the (in this case) book comes from an alternate future timeline, where you actually wrote the book, so the book doesn't actually come from nowhere.
Of course there's almost infinitely many alternative universes with the book scenario (ignoring the time travel for the sake of argument). One universe where you never finished the book, oe where it tanked, one where someone else wrote the story before you and you were a plagiarist, and x number of possible publishers, and so on...
And even with the time travel, you will have the option of not listening to your future self. You may see that there's a publisher who'll give you a better deal, and you might even see errors in the book you are given (since it is not really your work).
Alternate universes, sometimes called parallel universes, thinking may be a bit complex in some cases, but it does away with all time travel paradoxes and substitutes them with alternate versions of reality where any "paradoxical" event takes place, the "paradoxes" doesn't exist in the same reality.
I would argue that the "Bootstrap paradox" is really lazy plotting, and doesn't work at all, except with the alternate universes explenation. If you go back in your own timeline and give yourself a book, that book will never have been written in a single timeline universe. It would only work in that particualar case if your future self had actually stolen the book from someone else.
-Which neatly brings me back to the answer to the OP's question; Yes, it would be plagiarism in a single timeline universe.
I have always thought of this paradox as implying a single-timeline universe, and the fictional treatments of it usually deal with the inevitability of the known facts coming about - the narrative suspense comes from not knowing how they'll show up. ANUBIS GATES is a good example, but even better is Philip K Dick's PAYCHECK.
Here's the thing, though: when I was studying philosophy, though, I got to thinking about the free will implications. What if you had a perfectly accurate biography of yourself sent back through the past (we stipulate that the book is 'predictive', i.e. every proposition in it is unambiguously true, and refers to events in the past of the book's author, your future.) It would seem that, with free will, you are free to falsify those predictions. It says I had poached eggs for breakfast, so I fry them. The granularity of the predictions gets around the usual fictional dodge in which the prophecies can be brought about in unexpected ways. (It's hard to poach eggs by accident.)
It certainly feels like I could break the prediction, just in terms of role-playing it in my head. That would certainly imply that there isn't a single timeline.
The theory we're arguing against if we're talking free will is determinism, in which one's actions are determined by some set of causal factors interacting with the complex and devilishly handsome mechanism that is myself, but in a theoretically predictable way. The predictive book could have been the product of a Laplacean calculator at the beginning of time, or the omniscient mind of God at any point, says determinism. And the existence of the book, and our knowledge of it, becomes just another factor in the set of causes. Determinism still applies - I fried the eggs because the book caused me to.
(I like poached eggs much more than fried eggs. The only time I'm going to fry myself an egg is if I wanted to prove a point to myself about free will, which itself is a causal factor.)
Still breaks the single timeline though, eh? The poached-egg future can't exist, so the book wasn't predictive, so the whole thing is impossible if my thought-experiment about frying them is true. What I started to think was that, no, we don't have free will, unless there's some kind of randomizer at work in our heads (this is usually the point where the word 'quantum' makes its first appearance.) I actually like the idea that we're deterministic beings, because it means there are reasons for the way I act. It's surely better to be a weathervane than an Pop-O-Matic.
So yes, philosophically, I think what this paradox tells us is (a) free will is an illusion we're probably better off without and (b) time travel needs multiple timelines to avoid paradoxes. But fictionally? Alternate-timeline time-travel stories lack a shape. A paradox is an interesting shape that implies story; an alternate-timeline world that avoids paradox is just another place with less-convenient transport links.
