There are ways to restore files, deleted from the system by default, I'm not sure about the way they work but I guess thet read content, that has not been overwritten. On the other hand, there are programs (e.g. TrueCrypt), that encrypt disks, claiming that it wouldn't be possible to tell apart random data and file contents on such a disk without a password. Therefore I think that files, deleted from such disks can't be restored. Is that correct?
I know one way to find out would be to try it, but there is a possibility, that I would just pick the wrong restoring software. Moreover, I'm more interested in theorethical explanation why it would/wouldn't be possible. Thanks