What am I meant to do with Elder Scroll (Dragon) after completing Dawnguard?

There is a bug in the game where if you buy back the Elder Scroll (Dragon) from Urag gro-Shub after earlier selling it to him, you won't be able to sell it to him again after completing the final Dawnguard DLC main quest, Kindred Judgment.

The bug is fixed by the Unofficial Skyrim Patch. Download links: Original / Legendary Edition - PC / Special Edition - PC / PS4 / Xbox One.

Related patch note:

UDGP v1.2.3 - (2013-06-29)

After completing Kindred Judgment, it is not possible to sell the Dragon Elder Scroll back to Urag. This has been corrected. (Bug #12490)

The Dragon Elder Scroll is used as part of the main quest. Paarthunax will tell you to go retrieve it if you haven't done the dawnguard quest that makes you get it. I imagine it won't let you sell it so that you will have it on hand when you get to that point in the main quest. (Note: By "the main quest" I mean fighting Alduin)