office 365 – Someone shared a OneNote document with me through Microsoft OneNote Online: how can I add it in my OneNote account?

Someone shared a OneNote document with me through Microsoft OneNote Online: how can I add it in my OneNote account?

Use case: I don’t want to lose the file if the other person removes their OneNote document, or close their associated Microsoft Office 365 account (e.g. which happens when employee leaves a company).