The Codex: An Angel's Guide to Seducing a Human by Joe Duck

Goodreads Synopsis
When an ancient book capable of summoning a demon is stolen from heaven, Narius, a young and not so bright angel of knowledge, is cast down and ordered to destroy it.

If he fails, he can never return to his blissful life as a lazy library guard.

Fortunately, to aid him in his quest, Narius is accompanied by the Codex, a theoretically holy book, who sprouts terrible courtship advice like a cheap fortune cookie.

Upon arrival to the world below his, Narius is tricked into helping Emily, a greedy sorceress in a bit of a pickle, trying to deal with a hungry dragon.

Together, the human and the angel must overcome enchanted apples, evil elves and the impoverished dragon or risk watching their world burn.