Prepare
A half turn on all, odd or even pages. When the backs of a duplex scan are upside down, rotate only the even pages by 180 degrees and the file reads straight.
Turn just the even pages when a duplex scan flipped them.
A half turn keeps the page size and the position of everything on it.
The rotation is a page attribute; content is untouched.
The defaults come from your file. Change a setting and the proof updates before you let go of the mouse.