via itunes . Connect idevice to itunes, locate idevice in itunes, go to Apps section, at the bottom all apps are listed that can share content from and to the idevice.
keynote,numbers and pages are all sharing enabled. Just click the "add files" and navigate to your document you want to import.
Then when you launch numbers on the idevice, go to open document "from itunes" and there you will have the ones you added before.
I followed your instructions to transfer a Numbers file to my iPad. However, the part about choosing the Numbers app in iTunes (under File Sharing) then "add files" to look for the .cvs file created in Numbers did not appear on my iTunes. That is, there was no option to "add files". Maybe it's in a place I haven't looked. Would you know where I can find this?