When you save the document, where does it go and how do you retrieve it?

When scanning documents in the Notes App(per the support document you posted from), they are saved in the Note that was opened when you scanned it.

You can if you want to, export them from there to an other App or into a drive or server through the Files App if you want to by opening the scanned PDF and tapping on the share icon (arrow coming out of a box) , and selecting an option from the menu that appears.

That question is answered when you save the document. You are told where it’s going and may be offered some choices.

Of course, we don’t know the details since you haven’t told us exactly how you got to the point of being offered the opportunity to save this document.