USB to iPad supports only "Camera" files via camera connection kit.
There are lots of ways of moving files.
A simple and popular way to copy files and share files amoung your devices.
https://www.dropbox.com/
Using iTunes to transfer files:
http://support.apple.com/kb/HT4094?viewlocale=en_US&locale=en_US
Files Connect -- The swiss army knife of remote file connect
https://itunes.apple.com/us/app/files-connect/id404324302?mt=8
iExplorer -- " iExplorer's disk mounting features allow you to use your iPhone, iPod or iPad like a USB flash drive."
http://www.macroplant.com/iexplorer/
Windows File server
http://itunes.apple.com/us/app/filebrowser-access-files-on/id364738545?mt=8