I want to try before I buy, but I installed the codec, retarted, then installed the plugin, restarted, and nothing happened 
I have checked in the settings and it says Ardfry is installed on my computer, as well as in DO. I'm not sure what to do now. Searching DO forums, I found nothing, and the Ardfry site has no help files for this.
Does their plugin show up in Opus's list of viewer plugins (in Preferences -> Plugins -> Viewers)?
When you say "nothing happened" what are you expecting to happen? What kind of file are you trying to view? Have you tried the sample file that I think comes with the plugin and/or codec?
You can contact Ardfry here (found on their website): ardfry.com/Contact.html
By "nothing happened," I meant the function of the plugin, to enable the viewing of EPS and AI in the viewer, did not work. The EPS, and AI files I should be able to see in the preview do not show still. I have reset multiple times.
I have contacted Ardfry, and they are not sure what to do. They asked me to check if the trial still has days on it (it has 15 days left), and if thumbnails for AI, EPS, and PSD work in Explorer. They do, but I use DO. I have returned their email.
I asked here since I thought perhaps there is a setting in DO I have missed or overlooked.
There was only an exe for the codec - I will try to find the sample image you mentioned.
Does their plugin show up in Opus's list of viewer plugins (in Preferences -> Plugins -> Viewers)?