It is enabled if an external object has been selected and if you have the security profile EXTERNAL OBJECT ADMINISTRATOR with Inquiry rights or if security rights have already been granted and a record for this exists on Doc_Obj_Security table with 'View Current' or 'View All' rights. Clicking on View/Play will open up the applicable file for viewing.
When the object has more than one file name, a list box appears containing a list of file names and stores for the object of which one must be selected for viewing/playing.
If there is only one store and file name the selected object will be viewed/played immediately.