If you have an iPad Pro with a USB-C connector, that is Pad Pro 11-inch and iPad Pro 12.9-inch (3rd Generation), you just need to buy a suitable USB drive and plug it into your iPad directly. Note that iPad Air and iPad mini in 2019 comes with a Lightning-to-USB cable, so you don't need to buy another one. To connect USB devices to your iPad, you need an Apple's Lightning to USB Camera Adapter or third-party adapters. If your iPad is any model of iPad mini/Air, iPad Pro released before 2018 like 10.5-inch iPad Pro that is equipped with lightning connector, you'll not be able to plug a USB drive directly into your iPad since these iPad models don't have a USB port. It also supports transferring files between your iPad and USB flash drive. When you connect a flash drive to your iPad, the Files app will read files from your flash drive. With the new iPad operating system iPadOS, you can see an improved Files app that can help you manage files on iPad. Two models of iPad Pro in 20 - 12.9-inch iPad Pro and 11-inch iPad Pro, came with a USB-C port, which means you are able to plug a USB drive, SD cards, and external disk drive directly into your iPad.