When taking pictures on Lumia 1520 using Lumia Camera 5.0 with "Rich Capture On", a NAR file was also created. What is this NAR file ? I can't open it.
Those are Rich Capture files and when you select best shot it outputs your choice as a .jpg. Save those files; if you ever want to edit via Rich Capture on your phone you will need them.
If you want to... copy one to your PC and open it as a .zip to see inside.