A simple way to do this is to add a Custom Office button with the Program option, Module set to [External Program] and point to a .txt file that has one line of syntax similar to this -
{stp(UDF_DRAWING_FILE$)}"".pdf""
If your drawing files don't all share the same file extention then that would need to be part of the UDF data. Then align your button next to your UDF and the button will launch your document with the associated application. If you misspell the file name you see the attached message.