Do I need a special plug-in to convert DRM locked WMA files?
You don't need a plug-in but in trial mode, the application has some limitations like:
1. The output audio file is limited to only one minute.
2. There will be watermarks on the output video files.
And you need to have the rights to play the video (in other words if you can't get it to play in Windows Media Player, then you won't be able to convert it).