C#中打开word 文件并在richTextBox中显示

void OpenNewChildForm()        {            OpenFileDialog ofd = new OpenFileDialog();            ofd.Filter = "(文本文件)|*.txt|(word文件)|*.doc";            ofd.FilterIndex = 1;            if (ofd.ShowDialog(this) == DialogResult.OK)            {                MDIChild child = new MDIChild();                child.Text = ofd.FileName;                child.MdiParent = this;                // 如果打开的是 word 或者是 .txt 文件，就执行下面的代码；                if (ofd.FilterIndex == 2 || ofd.FilterIndex == 1)                {                    Word.Application wordApp = new Word.Application();                    Word.Document doc = null;                    object missing = System.Reflection.Missing.Value;                    object fileName = ofd.FileName;                    object readOnly = false;                    object isVisible = true;                    object index = 0;                    try                    {                        doc = wordApp.Documents.Open(ref fileName, ref missing, ref readOnly, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref isVisible, ref missing, ref missing, ref missing, ref missing);                        doc.ActiveWindow.Selection.WholeStory();                        doc.ActiveWindow.Selection.Copy();                        IDataObject data = Clipboard.GetDataObject();                        child.rtbChild.Text = data.GetData(DataFormats.Text).ToString();                        child.Show(); //子窗体的显示；                    }                    catch                    {                        if (doc != null)                        {                            doc.Close(ref missing, ref missing, ref missing);                            doc = null;                        }                        if (wordApp != null)                        {                            wordApp.Quit(ref missing, ref missing, ref missing);                            wordApp = null;                        }                    }                }            }        }

对于 .txt文件也一样适合；