I did not expect to find a missing feature in Directory Opus, but I did.
When I try to drag-drop a file from within an archive folder (ie. rar,zip,) I can't drag-drop these files onto another application. From for instance Winrar I can pick up a subtitle file and drop it on my MPC media player and the subtitles are loaded. When I try to do the same from dopus I see a not allowed icon. Now I have to open the right panel, navigate to a temp folder, copy the file and pick it up from there. Not a problem, but when you have to do this often while you were used to do it faster it gets annoying.
You should be able to drag the files to e.g. Windows Explorer, which is another program, proving that it can work.
The fault may be with the program you are trying to drag to only supporting one type of drag data. Some applications only let you drag files which are already on disk and don't support virtual files / streams. All programs that support drag & drop should support streams, as they are quite common and often far more efficient for files which don't exist on disk. They also allow the drop target to manage the lifetime of its temporary files (if it needs to write the information to disk, which it often does not).