I dont know about a wired keyboard but I have a Bluetooth Keyboard connected to my iPad Mini and it works great. I have the Amazon Basics Keyboard and it connects almost instantly when I turn it on and hit shift.
The only way I have heard that you can get a USB stick to work on a iPad is to Jailbreak, use a powered USB hub, and use a Lightning to USB (Camera Connection kit for older devices) connector to hook everything up. You might also run into power problems because the power that the iPad uses to read USB devices has been lowered.
IMO not worth the hassle and better to just email documents, or put them in Google Drive (5GB free) or a similar service.