You don't open in the DNG converter. You use it to batch convert, folder by folder, and the converted copies can then be opened in the ACR version you have.
Two things to watch: One, don't try to convert single files, it won't work. The DNG converter operates on folders. Two, set the compatibility level to the ACR version you have.
If it still doesn't work, the files may have been corrupted by an early version of Nikon Transfer (later versions fixed). There is a utility to "uncorrupt" them if that's the case (Google it).
Thank you. The instructions for the DNG converter are not very informative for this. I navigated to the folder, which appeared to be empty. I ran the folder, and the converted images appeared.