It sounds like the document was corrupted in iCloud. I'm sorry you could not recover it.
It might be possible to recover it.
You don't say what kind of computer you use, if any. I it is a Mac and you sync it to iCloud, then all iCloud documents are mirrored in a system folder, and will be backed up by Time Machine (again, if you use it). Unfortunately, documents are not synced on a Windows machine, so there will be nothing in any backups you do there.
Apple Support may be able to restore the document, or more likely the entire document folder, from their server backups. This would take time, and if you do not have AppleCare it will cost money. Still, if the document is that important.
For my last, a bit of advice. Don't depend on the iPad to be the only place you keep important documents. iCloud can not be considered a backup, because it updates quickly and does not keep a history of prior versions. I use a free Box.com account to back up my important iWorks documents. The service has WebDAV support which makes less trouble to use with iWorks than DropBox, though they are also usable for this purpose.
Anyway, after I update an important document, I take the extra 15 seconds to update it on Box. Not ideal an ideal solutions, but the best I've come up with for now. Well, besides the backups that happen automatically on my Mac. But restoring from that is a bit of a pain, so I reserver it for real problems. Besides, three copies is even better than two for security.