Classic office scanner moment, happens to us every other week. The viewer only rotating the display is a common trap. I use a free online PDF converter called Convert2PDF for this, it has a Rotate PDF tool where you pick specific pages and turn them by 90 degrees, then download a properly fixed file. Page previews show you which ones are sideways, so you don’t have to guess. If the scanner also mixed up the order, there’s a Reorder Pages tool right next to it. It’s all in the browser and the contract stays on your computer, which I’d care about with a client document. I keep it bookmarked now, because some scan always comes out crooked. Took me about five minutes for a similar 40-page mess.