mxd文件批量更换版本

public void ChangeBB(string filePath,string fileName)
        {
            IMxdContents pMxdC = axMapControl1.Map as IMxdContents;
            IMapDocument pMapDocument = new MapDocumentClass();
            pMapDocument.New(string.Format("{0}/{1}",filePath,fileName));
            IDocumentVersion docversion = (IDocumentVersion)pMapDocument;
            docversion.DocumentVersion = esriArcGISVersion.esriArcGISVersion93;
            IActiveView pActiveView = axMapControl1.Map as IActiveView;
            pMapDocument.ReplaceContents(pMxdC);
            pMapDocument.Save(true, true);
        }