setting page breaks?

How do I change the page breaks when in preview?

If you’re speaking of LibreOffice Writer, it probably isn’t appropriate to create page breaks in preview. While there is a simple page break function, there is also a page break function that allows switching the page style as well as resetting the current page number. In general, a page break is a code set in a document ie. a part of it’s content. Preview is showing how the document would format using the current printer settings. Preview isn’t the place to change a document contents.