A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
One suggestion I can give is, instead of using Insert > File Printout, open the file first and then use Print command in the application (e.g. Adobe) and choose your orientation there. This will do the same insertion, but with the correct orientation.
I had this same problem. Adobe (and other pdf software for that matter) would display my documents on the screen properly in landscape mode, but they would display the documents sideways when printing to OneNote.
I would only further clarify the advice above that says to choose the orientation (landscape) while printing. Do this by selecting "print" from within your pdf software, selecting "OneNote as your print destination, BUT ALSO click PROPERTIES and check "landscape." For me it would then print properly to OneNote in landscape orientation. Just elaborating a bit on the excellent solution above