iPad Pro usb
Can you use a USB adapter on the iPad Pro 2018 to access documents stored in a flash drive?
iPad Pro, iOS 12
No. The iPad Pro (and other iPads) has no native capability to access standard USB drives.
There are special drives that can be used via their own App to read and write files to them. Some are wireless.
Currently there don't appear to be any USB-C drives that work with an iPad Pro however most compatible drives have the Lightning connector for older iPads.