Apple's iCloud Documents feature in iOS -- recently brought to OS X -- can be very handy for keeping documents in sync across all devices you use to access or edit them. It's an Apple-only feature for which there is no way to gain foreign access.
But that's OK. iCloud Documents is quite limited, requiring the same app on each device to read a particular file type. Many apps in iOS aren't on OS X, such as OS X's TextEdit text editor, so iCloud Documents often can't do the job.
You should use Dropbox or Box instead; many iOS apps support them natively, and they work on pretty much every mobile and desktop OS today.