C# 将word文档转换成PDF文件，出错：尝试读取或写入受保护的内存。这通常指示其他内存已损坏。

出错代码：_Document wordDocument = null;wordDocument = wordApplication.Documents.Open(
                                ref paramSourceDocPath, ref paramMissing, ref paramMissing,
                                ref paramMissing, ref paramMissing, ref paramMissing,
                                ref paramMissing, ref paramMissing, ref paramMissing,
                                ref paramMissing, ref paramMissing, ref paramMissing,
                                ref paramMissing, ref paramMissing, ref paramMissing,
                                ref paramMissing);if (wordDocument != null)  
                    wordDocument.ExportAsFixedFormat(paramExportFilePath,
                    paramExportFormat, paramOpenAfterExport,
                    paramExportOptimizeFor, paramExportRange, paramStartPage,
                    paramEndPage, paramExportItem, paramIncludeDocProps,
                    paramKeepIRM, paramCreateBooks, paramDocStructureTags,
                    paramBitmapMissingFonts, paramUseISO19005_1,
                    ref paramMissing);程序运行到wordDocument.ExportAsFixedFormat这里就报错：尝试读取或写入受保护的内存。这通常指示其他内存已损坏。
求解，很急！！！