With the camera adapter you can import photos and videos from USB to the iPad. I'm pretty sure you cannot export from the iPad to the flash drive. I'll defer to others regarding text and pdf files. Actually, I'll grab a flash drive and see what if any I can transfer.
For me what works best is putting all my files on a network hard drive MyCloud and then can access from any device in my home or from anywhere I can get on line.
Update: The flash drive didn't actually work at all to even download to the iPad - said it required too much power.