CRAXDRT.Report report;
            string pathReport = "C:\report.rpt";
            CRAXDRT.Application app = new CRAXDRT.ApplicationClass();
            report = app.OpenReport(pathReport, 1);

            CRAXDRT.SubreportObject subReportObject = null;
            CRAXDRT.Report subReport = null;

            for (int index = 1; index < report.Sections.Count; index++)
            {
                for (int index2 = 0; index2 < report.Sections[index].ReportObjects.Count; index2++)
                {
                    CRAXDRT.IReportObject reportObject = (CRAXDRT.IReportObject)report.Sections[index].ReportObjects[index2 + 1];
                    if (reportObject.Kind == CRObjectKind.crSubreportObject)
                    {
                        subReportObject = (CRAXDRT.SubreportObject)reportObject;
                        subReport = report.OpenSubreport(subReportObject.SubreportName);  //E qui ti ritrovi il nome del sottoreport e relativo oggetto