Abstract: The invention relates to a method for handling co-operation files, where the content of the co-operation files is of the type that describes the co-operation basis in relation to a co-operation between document owners and document users and where a unique hash calculated ID is attached to and embedded into a co-operation file, where the document owner stores co-operation files on a central file handling database and where the co-operation files of the document users are stored on a the user's computer. The method includes checking if a co-operation file exists on the central database with an ID matching the ID of the co-operation file stored on the document user's storage medium where the checking is initiated by the supplier trying to access the co-operation file stored on the document user's storage medium, and informing the user if a version of the co-operation file stored on the central file server differs from the version of the co-operation file stored on the document user's storage medium.