I have the similar question... I often have a pdn file open that is save, but need to save a jpg copy off. However, I then may need to go back, invisible the current layer, and visible another to save as a different jpg file. Since Paint.NET lands me on my newly saved jpg with the layers flattened, I have to close the jpg and re-open the .pdn file I was working on. Having a Notepad++-like "Save Copy As" would be very beneficial.