[GeoffR]

If there is not enough room to fit the full word on the line, then it is normal for left-justified books to begin the word on the next line, hyphenation is avoided if possible.

Perhaps you are comparing a book with full-justification to one with left-justification? full-justification often hyphenates in places that left-justification wouldn't. If that is the case you should be able to change the justification mode on the font menu. But some books are created in a way that forces left-justification, so for those books you would need to edit the book's CSS file to remove the "text-align: left;" lines from the paragraph classes used for the main text.

It could also be that hyphenation has been disabled in the book. If that is the case you would need to edit the CSS and remove the "adobe-hyphenate: none;" lines.

Edit: The choice of language also affects hyphenation, so another possibility is that the language has not been set correctly in the book.