File Extension USE File Format Source Integrity file (MKS) USE stands for Source Integrity file (MKS). 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 The March, 2010 launch of the new HP-UX 11i Operating System MKS implementer is not able to compile RPG program WITH clause not working.