TBH I think the best way would be to provide migration instructions for the users and let them handle it from there (if they so choose). As @OldManGeorge implied, there's very little of the process that can be automated, as most of it (export, import, open) takes place within the proprietary apps themselves. Also, OneNote has a rather useless and annoying import behavior in which it splits imported notebooks with over 100 pages into separate 100 page sections. This means you have to manually remerge large notebooks within the OneNote for Windows 10 application itself.
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