1)On the right panel there is single property called "Definition URL", Click on value then click "..." and select your conv file.
2)From inside stylus studio you can use either XQuery or XSLT to process multiple text files.
In the DataDirect XQuery user Guide, search for "Querying Multiple Files in a Directory", section "Non-XML Files"
Components\DataDirect XQuery\books\ddxquery\ddxqug\ddxqug.pdf
Similar task can be accomplished using XSLT and the doc function