The beta Cloud Provider option seen in earlier versions of OmniGraffle for iOS has been removed in the current releases, as OmniGraffle now directly integrates with the native iOS Files app. The functionality added by the Files app in iOS 11 replaces the functionality offered by our previous cloud storage beta, and makes it much easier to edit and sync files stored in iCloud Drive and other cloud providers, which is why it is no longer necessary for us to provide our own file provider or iCloud integration outside of this.
Since OmniGraffle 3 currently uses the same Files app for document management that you see in many apps across iOS, there aren’t any special instructions for using it that would be exclusive to OmniGraffle. (Similarly, OmniGraffle 7 for Mac relies on the Finder for all document management, but you won’t find documentation on how to use Finder in OmniGraffle for Mac user manual.)
However, if it’s helpful, Apple provides documentation on how to use the Files app on within their documentation of iOS on their site here: Use the Files app on your iPhone, iPad, or iPod touch
Thanks for sending that email — we’ll be happy to look into why your files aren’t opening, and discuss this further with you via email if you have any further questions or concerns, but I hope this explanation about why we made this change helps anyone else who comes across this thread.