In addition to Manual, Paragraph and Style page breaks there are two unusual ways that Word can insert a page break where you might not expect one. Keep with next and Keep lines together.
Word’s Paragraph settings have two Pagination settings which can insert a Page Break where required. Keep them in mind if you’re trying to work out why there’s a new page when you don’t expect it.
Both these settings are in Paragraph settings | Line and Page Breaks in the same place as Page break before. Either as a Paragraph setting or in a Style configuration.
Keep with next
This option forces Word to show this paragraph and the next paragraph on the same page.
It’s the default for Heading styles to ensure that a heading doesn’t appear at the bottom of a page with the next paragraph ‘orphaned’ at the top of the next page.
Keep with next has other uses such as the line before a list. Or keep lines together within the list, to ensure an item and sub-item stay together.
Keep with next, in some extreme situations, can force an unexpected page break. Too many adjoining paragraphs all ‘Keep with next’ will force Word to move them all to a new page.
Keep lines together
This option stops a paragraph being split over two pages.
If Word can’t fit the whole paragraph at the bottom of a page, the paragraph will be placed at the top of the next page.
For a long paragraph with that setting, that can make for a large gap at the bottom of the previous page which looks like a forced page break.