打开阿拉伯语的word文件乱码，求帮助...

private void openWordOrRtfFile(string fileName)
        {
            Word.ApplicationClass app = new Word.ApplicationClass();
            Word.Document doc = null;
            object missing = System.Reflection.Missing.Value;

            object FileName = fileName;
            object readOnly = false;
            object isVisible = true;
            object index = 0;
           // object encoding = Type;// UnicodeEncoding;

            try
            {
                doc = app.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();
                showContent = data.GetData(DataFormats.Text).ToString();
                MessageBox.Show(showContent);
            }
            finally
            {
                if (doc != null)
                {
                    doc.Close(ref missing, ref missing, ref missing);
                    doc = null;
                }

                if (app != null)
                {
                    app.Quit(ref missing, ref missing, ref missing);
                    app = null;
                }
            }

            return ;
        }

我用上面的代码打开word（里面是阿拉伯文）并显示在richtextbox或则messagebox里面都是问号，到底是为什什么啊，汉语没有任何问题，应该是编码的问题，open函数中怎么设置编码啊，我查msdn找不到这个函数..... --------------------编程问答-------------------- 高人呢......

补充：.NET技术 ,  C#