assign nothing as default open with application
RCDefaultApp - freeware, installs as a Control Panel. Yes, it's a million years old, yes it still works to Mojave, but may not at Catalina.

Extensions tab [might take a few seconds to populate], find your .asd in the list &amp; set the default to &lt;disable&gt;

New kid on the block for when RC is no longer viable seems to be SwiftDefaultApps though it doesn't seem to be so simple for this task.