AppearanceSprite->AttachParent = RootComponent; To attach the sprite to root component.
Then in your header file, make sure you have
UPROPERTY(EditDefaultsOnly, Category = "Sprite")
class UPaperFlipbook* AppearanceSprite;
To make sure, that you will be able to add the flipbook in editor for your actors. If you want to load flipbook object at runtime, then look into ConstructionHelpers, and how to load referenced objects in C++.