Documents in app

I am trying to update an iPad app that was purchase from another apple ID which was no longer in used. I went and purchased the upgrade app from my iphone which has a Family Sharing with the iPad. When I try to update the app in the iPad, it ask me for the apple ID that was no longer in used.

Question: If I delete the app in the iPad, will it delete all the documents that was used in that app?

If yes, is there a way to delete only the app but retain all the data so that if I re-install the upgraded app, I can still read all the old files on it?