I've moved all the files from the folder in the "Effects" folder of Paint.net. It worked the whole time, damn.
Edit: Now it works. I don't know why but I reinstalled it the third time and now everything seems to work. Thank you anyway!
I don't know why but it doesn't work anymore for me. After Avast deleted my current Nik Collection I had to reinstall it again together with the 8bf plugin.
When I want to start one of the filters I get this message.