There's no such things as a CS7 file.
A couple months before the InDesign CC release, the name was changed from CS7 to CC.
When you say InDesign CC, doo you mean the InDesign CC release from this year, or are you still using InDesign CS6 through a cloud subscription? There are a lot of users confused by this.
If you have CS6 through a subscription you are entitield to the new version for free and should go to creative.adobe.com and download the newest version of the Creative Cloud Desktop Application and get the new versions of the applictions you use.
And should you have a perpetual license for CS6 the answer is you don't. The CC file needs to be exported or saved as IDML.