How are widows and orphans handled?

Widows (a lone last line of a paragraph stranded at the top of a page) and orphans (a lone first line stranded at the bottom) look amateurish in a printed book. The Interior Formatter handles them for you, adjusting the pagination so lines don't get stranded — the same courtesy a human typesetter applies.

This is one of the reasons your page count and line breaks differ from your Word document: the formatter is making dozens of small professional adjustments to keep the type clean. You don't need to do anything — it's automatic.