The CDF_DOC procedure retrieves general documentation information about a Common Data Format file.
            Examples
            id=CDF_CREATE('VersionCheck')   
            CDF_DOC, id, vers, rel, copy, INCREMENT=incr
            PRINT,'File Written Using CDF', vers, rel, incr, $
               FORMAT='(A,I1,".",I1,"r",I2)'
            CDF_CLOSE, id 
            IDL Output
            File Written Using CDF2.6
            Syntax
            CDF_DOC, Id, Version, Release, Copyright [, INCREMENT=variable] 
            Arguments
            Id
            A CDF ID, returned from a previous call to CDF_OPEN or CDF_CREATE.
            Version
            A named variable in which the version number of the CDF library that created the CDF is returned.
            Release
            A named variable in which the release number of the CDF library that created the CDF is returned.
            Copyright
            A named variable in which the copyright notice of the CDF library that created the CDF is returned.
            Keywords
            INCREMENT
            Set this keyword to a named variable that will contain the increment of the CDF library that created the specified CDF file.
            Version History