What? No wait, you don't understand what i meant.
I always save my file in pdn format, thats clear. If you save the pdn as jpg, gif or whatever Paint.net is then using the saved file and not the original pdn. What i want is this - a new File -> Export as ... Option where the pdn is saved in a new file bute Paint.net is still using the pdn after that. So it would be possible to use the new jpg, gif or whatever in my project environment but still working on the pdn without closing an reopening the file.