Locate the Rotate View submenu and choose either "Clockwise" or "Counterclockwise" to rotate the page view in 90-degree increments. This reorients pages from portrait to landscape, or vice versa.

Learn how to rotate just one page of a multi-page PDF in Preview.

With the Option key held down, only the current page will rotate. (If you save the document, it will be saved with the single page rotated.) Rotate single PDF pages in Preview [Mac OS X Hints] ...