Old DLC are not in .AP, but were distributed in several required blueprint sub-folders.
New third parties DLCs are still being distributed in several sub-folders (for example Machine Rail steam locomotives).
I ignore why is that. May be the .AP format is something that has copyrights by DTG?
The problem comes when you are start modding as you need to edit the distributed files. If you have .AP files all your mods will stay outside of the original files.
.AP compressed files are just .ZIP files that you can open with Winzip, .RAR or .7z.
So it is very simple to have a working .AP. The way I do, is compressing all the folders being distributed, using Windows right click (Compress to). Once I get the .ZIP file I rename .ZIP to .AP and then I delete all outside subfolders. It works with RAR and 7Z and probably all similar compressed files.
Once you have your own .AP all modding will be located outside the .AP.
I suggest to remember making your .AP with only the third parties distributed files (no older mods included).
I hope this helps someone.
