Using a second my Apple ID on my Dad's iPad
My Dad is letting me borrow his iPad for a while. I want to preserve his Apple ID, so he can purchase things on Amazon and such. At the same time, I also want to use the iPad to purchase things for myself, as well as be able to use it as a second monitor for my MacBook Air. I think that requires both devices to be using the same Apple ID, right? So, how do I set up my Apple ID as a second one on his iPad? I do not want to reset the iPad and eliminate all his apps and data. Please let me know your thoughts. Thank you!
iPad Pro, iPadOS 16