visual studio 2012操作word 时发生 “wordDoc.Activate();未将对象引用设置到对象的实例。”异常

Question

   //通过一个标签读取word的内容
        public string reading(string bookmark, string path)
        {
            wordApp = new ApplicationClass();
            wordApp.DisplayAlerts = WdAlertLevel.wdAlertsNone;///////////////////////??????????????????
            wordApp.Visible = false;
            object missing = System.Reflection.Missing.Value;
            object templateName = path;
            wordDoc = wordApp.Documents.Open(ref templateName, ref missing,
                ref missing, ref missing, ref missing, ref missing, ref missing,
                ref missing, ref missing, ref missing, ref missing, ref missing,
                ref missing, ref missing, ref missing, ref missing);
               
            wordDoc.Activate(); 
          object bq = bookmark;
    
         Bookmark mbook =  wordDoc. Bookmarks.get_Item(ref bq);
           
        //   object range = wordDoc.Bookmarks.get_Item(ref bq).Range;
       //  Paragraph wp = wordDoc.Content.Paragraphs.Add(ref range);
            if (mbook.Name.Equals("duanluo2"))
            // MessageBox.Show(wpReadingOrder + "qqq" + mbook.Parent + "hjdjs" + mbook.Range + "aaa" + wp.ID);
            {

        mbook.Range.ShowAll = true;
                mbook.Range.Select();
                mbook.Range.WholeStory();
                mbook.Range.Copy();
                MessageBox.Show("dgasf");
                IDataObject data = Clipboard.GetDataObject();
                string test = data.GetData(DataFormats.Text).ToString();

                MessageBox.Show(test);
            }
            return "";
        }