All the apps you had and paid for are all tied to that original Apple ID.
If you go back to using that Apple ID, you can retrieve all of your apps that you had on that iPad.
Other than that,
A 4th gen iPad is a nearly 7-1/2-year old device, now!
Its internal hardware is too old, underpowered and completely incompatible with any current and future versions of iOS.
As of the beginning of 2019, many, MANY third party app developers are all more quickly and completely dropping older app support for all old 7, 8 and 9-year iPads that are running 2-3 year old and earlier iOS versions.
Third party app developers are removing all of their older, legacy versions of their apps from Apple's App Store servers, now.
Older versions of apps are going to be gone for good, now!
Getting older versions of app for these old iPad models, initially from Apple’s iOS App Store is getting to be very difficult and problematic, now, and will only be getting much worse in the year 2020.
These old iPads are now reaching their complete end of life and support.
Old iPads that can no longer be upgraded/updated will have NO MORE APPS AVAILABLE for initial download, at all, soon, from the Apple iOS App Store, for such old iOS devices in the very near future.
Older versions of apps for older iPads will be completely gone, very soon!
Time to now seriously consider a new or discounted, refurbished iPad from Apple.
Sorry & Best of Luck to You!
