Sorry, you only options are to get a subscription to InDesign CC, or to have an InDesign CC user save backwards in an IDML file you can open.
There's no other way.
Compatibility will depend on application. InDesign for instance needs to be saved back via IDML. But it will be the responsibility of the Creative Cloud user to take care of this for the most part.
For InDesign, Markzware has a new tool: http://markzware.com/products/markztools/
I suggest posting in the various application forums to find out details on compatibility.
Keep in mind that Creative Cloud will become more and more incompatible with CS6 and earlier versions as time goes on and features are added to the software.
@Bob, and the wonderful irony is that Markzware's plugin is available via subscription only.
I only have had one customer for which I needed CC for, and that was another designer I picked up their overflow for a single job. I was able to just use the 30-day trial version for it. But if I had a client that was using it, I wouldn't hesitate to rent Conscription Cloud, er, Creative Clown...dang fingers...Creative Cloud. If it's a paying gig, there's little reason not to in my opinion.
Using the plugin from Markzware might work well. Dunno. Wouldn't even purchase it if it was a perpetual license. It has always been better for everyone to be using the exact same version of ID. Most of my ID clients are still using CS5.5, some on CS6. I have no compelling reason to rent by the year or month to month until such time as a client is using it.
There’s nothing ironic about it. Subscription software is not going away and more and more will go in that direction.
Whatever regarding subscription software. Only time will tell. If Adobe ever reaches 12 million subscribers I'll be the first to admit it works for them. It isn't working that great for some other companies I am aware of, and personally, I don't think it is working that well for Adobe.
The irony is that the OP doesn't want subscription software. It was ironic to point them to subscription software.
I guess the markzware solution would be the least expensive. But again, I really did not want to rent software. I do appreciate all the input on this. Even the typos.
I do not get alot of those files from the cloud version, it just would be nice to not have to ask the customer for the backward compatable.