External files (with .nds extension) are created by NDS each time a recipe is saved, containing a snapshot of the recipe with all its accessory data (animal inputs, feeds, mixes costs etc.). The owner of the file can give it to other users that can open it and review its contents, modify them and, possibly, carrying them in their systems with the getting inside feature. On the contrary, the Import-Export feature produces a file that can store more than one recipe, but cannot be opened before import.
From the release 3.8.6.01 a farm export produces a file that can be opened and modified like an external file, or regularly imported like an import file.