File Extension OPX File Format Extension DLL (OPL) OPX stands for Extension DLL (OPL). This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Error message: DLL undefined VBD file not loading in IE9 How can i make only one administrator to accsess database through C# application,and without registering this administrator in atable in the database?