There are wireless, WiFi built-in hotspot transmitter hard drives/flash drives that you can use with that 4th gen iPad.
These are made by Western Digital, Seagate and Sandisk.
These drives have proprietary iOS apps that you must use with these drives.
Wifi transfers on these drives are slow, but still will transfer the data from iPad to wireless drives.
These are the ONLY drives you can use with a 7-year old iPad.
I use two SanDisk connect drives with my iPad Pro still running iOS 10 ( as your iPad 4th gen should be using ) and these work.
I, also, use a portable, Seagate wireless, built-in WiFi hot spot hard drive that, also, works with my iPad Pro running iOS 10.
Western Digital makes a similar drive to Seagate’s.
Good Luck to You!