The ipad doesn't support output to a flash drive. You need a third party app. Never heard of an apple flash drive. Must be a third party drive sold via Apple.
For anything important, you should backup copies. What if someone stole your flash drive? I would use some type of syncing service to backup your papers. Read in the local paper a while back where someone stole a ladies backpack. Contained a flash drive with the only copy of her masters thesis! The criminal used her credit card. She went dumpster diving at every store where the credit card was used. She found her backpack with the flash drive in it! Hence the newspaper report. Don't go dumpster diving.
You could try Microsoft onedrive(?) a cloud based storage device.
You could try a wifi storage device. Believe you have to save the file first then move it to the wifi drive.
Airstash
"Easily access, transfer, and stream your files from AirStash® – the pocketable wireless flash drive for iPad, iPhone, and iPod touch! This app requires an AirStash device in order to work. View, import & export photos, wirelessly stream videos, music & podcasts, and view documents stored on your AirStash. AirStash+ is an enhanced alternative to the built-in web interface adding features only possible with a native app."
http://www.airstash.com/
SanDisk
" SanDisk Connect Wireless Stick is the flash drive reinvented to work with both your computer and your mobile devices."https://www.sandisk.com/home/mobile-device-storage/connect-wireless-stick
Seagate Wireless portable hard drive
"The new 500GB Seagate Wireless portable hard drive is the company's latest HD designed specifically for use with tablets and smartphones like Apple's iPad and iPhone."
http://www.macrumors.com/2015/01/04/seagate-ces-2015-new-products/
Allows you to access your own sd card and usb device
http://www.amazon.com/Dane-Elec-Media-Streamer-Mobile-Junkie/dp/B00IA8LLUW
suggested by seeblue
http://www.dpreview.com/forums/thread/3516024
Camouflage data files as a raw image.
read files from a flash drivehttps://www.youtube.com/watch?v=m5f1VmjjczQ
Kingston Digital MobileLite Wireless Flash Reader for Smartphones and Tablets (MLW221)
Kingston Digital MobileLite Wireless Flash Reader for Smartphones and Tablets (MLW221)
CloudFTP
https://www.kickstarter.com/projects/danielchin/cloudftp-wirelessly-share-any-us b-storage-with-ipa
https://www.amazon.com/HyperDrive-iUSBport-CloudFTP-Storage-Wireless/dp/B008U9GS 18