I found some information on the web after all. The most useful was this article, even if it's a bit old:
http://www.ilounge.com/index.php/art...ta-protection/
And this one was interesting too:
http://www.csoonline.com/article/268...-features.html
I still don't understand it all, but I think that if:
- the document is stored in an app that uses the iThingie's hardware encryption (usually activated through the app's options)
- your iThingie is password protected (meaning that hardware encryption has been activated)
- the document is not visible in iTunes app sharing
- the document is NOT synced to iCloud
then it's reasonably well protected.
That's enough for me I guess, I don't carry state secrets on my iPad.