public void Dispose()
 {
     if (DocReader != null)
     {
         DocReader.Close();
         DocReader.Dispose();
         DocReader = null;
     }
 }
        public static void Open(string fileName)
        {
            if (string.IsNullOrEmpty(fileName) || !File.Exists(fileName))
            {
                CustomMessageBox.Show("您要打开的文件不存在,请确认操作!");
                return;
            }
            Close();
            Application.Current.MainWindow.WindowState = WindowState.Minimized;
            string fileType = Path.GetExtension(fileName).ToLower();

            switch (fileType)
            {
            case ".doc":
            case ".docx":
                DocReader = new WordDocumentReader {
                    FileName = fileName
                };
                break;

            case ".xls":
            case ".xlsx":
                DocReader = new ExcelDocumentReader {
                    FileName = fileName
                };
                break;

            case ".pdf":
                DocReader = new PdfDocumentReader {
                    FileName = fileName
                };
                break;

            case ".dwg":
                DocReader = new CadDocumentReader {
                    FileName = fileName
                };
                break;

            default:
                DocReader = new UnknownDocumentReader {
                    FileName = fileName
                };
                break;
            }
            DocReader.Open();
            DocReader.Activate();
        }