I currently have Photoshop CS6 along with Lightroom 5 installed on my PC. I've just bought a Canon camera product that comes with a 1 year free subscription to Photoshop CC. If I upgrade for the 1 year free subscription, and then cancel it after the 12 months has elapsed will I be able to open the Photoshop CC PSD files in Photoshop CS6?
Several features (Liquify as Smart Filter, Filter Gallery as Smart Filter, …) will not work in CS6 but you should be able to open the files in Photoshop CS6 (if you will have saved with Maximized Compatibility at least) with the affected Layers rasterized.
This compatibility guide gives more information on how to move files between CC and CS6 for all Adobe applications, including any sticking points or things that won't work perfectly:
Hope that helps!