No! Not acceptable! Not just because it is "poor" condition in bookselling terms, but it is almost 100% likely to be a "destroyed" copy and thus stolen goods! Recycle it for the paper.
[For those that don't know] Booksellers can "return" unsold mass-market paperback stock by just sending the cover back to the distributor, and destroying the rest of the copy. Saves shipping costs, which would be more expensive than the book is worth to return the whole thing. Not destroying the rest of the book and selling it on is stealing.
Definitely mold because of the circular shapes, it has been growing there for a long time. Wherever they stored it, you could start growing beautiful mushrooms there.
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