I found this post, which leads me towards what I need: How to link to external files with relative path in QGIS actions?
Now, I'm trying to use the eVis plugin to open .DWG and .DXF by launching AutoCAD from the Event Browser. I've tried to configure the external application as shown in my screen capture. The file name is now highlighted in green under the Display tab, but nothing happens when I double click on the file pathname. I'm using relative paths. I've tried modifying the extension to not include the '.' and it doesn't work either. There are issues with opening the pdfs in Foxit as well. Any insight would be appreciated!