As Barry states, there is one orientation for the entire document. That doesn't prohibit you from inserting/pasting an object (e.g. Numbers spreadsheet, or Pages Table, Chart, PDF, Shape, Image, or Text box, and from the Pages v6.1.1 Arrange tab — changing the rotation of the object on that single page. You cannot rotate body text on a page.
Here is a thumbnail section from a Pages v6.1.1 document where I pasted a PDF best image of three Pages tables, and then rotated it 90 degrees. These tables fit in portrait mode just fine, but I rotated them here for illustration purposes.
