documentID to source?

You have to modify the namespaces and the exact property names for you purpose, but this can easily be adapted for your purpose:

Hope it helps.

#target bridge
if( BridgeTalk.appName == "bridge" ) {
DocumentIDToSource= MenuElement.create("command", "Document ID to Source", "at the end of Tools");
}
DocumentIDToSource.onSelect = function () {
    loadXMPLib();
    //
    var sels = app.document.selections;
    for(var a in sels){
        if (sels.spec instanceof File && sels.name.match(/\.(cr2|raw|dng|nef)$/i)) {

            var xmp = new XMPMeta(sels.synchronousMetadata.serialize());

            // try another namespace to get other simple properties:
            var DocumentID =  xmp.getProperty("http://ns.adobe.com/xap/1.0/mm/", "DocumentID");
            // If you are getting "localized text properties", use instead this one:
            // var Description =  xmp.getArrayItem("http://purl.org/dc/elements/1.1/", "description",1);
            // settting localized text property
            xmp.setLocalizedText("http://purl.org/dc/elements/1.1/", "TransmissionReference", null, "x-default", DocumentID);
            // setting simple property
            // xmp.setProperty("http://purl.org/dc/elements/1.1/", "NewProp", "my prop value");
            //
            var updatedPacket = xmp.serialize(XMPConst.SERIALIZE_OMIT_PACKET_WRAPPER | XMPConst.SERIALIZE_USE_COMPACT_FORMAT);
            sels.metadata = new Metadata(updatedPacket);

        }
    }
    //
    unloadXMPLib();
    // Functions needed:
    ///////////////////////////////
    function loadXMPLib() {
        if ( xmpLib == undefined ) {
              if( Folder.fs == "Windows" ) {
                  var pathToLib = Folder.startup.fsName + "/AdobeXMPScript.dll";
              } else {
                  var pathToLib = Folder.startup.fsName + "/AdobeXMPScript.framework";
              }
              var libfile = new File( pathToLib );
              var xmpLib = new ExternalObject("lib:" + pathToLib );
        }
    }
    ///////////////////////////////
    function unloadXMPLib() {
        if ( ExternalObject.AdobeXMPScript ) {
            try {
                ExternalObject.AdobeXMPScript.unload();
                ExternalObject.AdobeXMPScript = undefined;
            }catch (e) { }
        }
    }
};

I do know the purl namespace will have to be changed to something else—I left it there as a placeholder for when I have the right information...