Considering these points, the best feature could be a legal resource hub that helps users find where to purchase or access "Jazz" in PDF format, includes study guides with permission, and offers citation tools or discussion forums for book clubs or students. It should avoid any unauthorized distribution of the book itself.

Also, the "upd" part might refer to updates or the latest editions. So maybe the feature could check for updates or new editions of the book, notifying users when a new version is available. But Morrison's "Jazz" is a classic, so updates are unlikely. However, maybe different editions (like annotated versions) could be featured.

So, possible features could be an online reader with annotations, a download option after verification, or integration with libraries. However, I should consider copyright laws here. Toni Morrison's works are copyrighted, so distributing the full text without permission would be illegal. The user might not be aware of this, so the feature needs to respect copyright while providing value.