macOS High Sierra
in the toolbar, then select or deselect the “Show page numbers” checkbox.If you see an alert (red triangle) while working on a book
If you see a red triangle with an exclamation point while working on a book, there’s text that doesn’t fit in the available space, either because the font is too large or the text uses too many characters.
Add, remove, and reorder book pagesAdd and remove photos in a book