使用visual studio 2008的互操作词库从word中读取特殊字符，如ρ，λ

我正在使用visual studio的Microsoft.Office.Interop.Word.Document库阅读word文件。问题是文件包含特殊字符，如ρ，λ。当我在c#中阅读时，它们被转换为?问号。
例如，我正在读这样一行A child drinks a liquid of density ρ through a vertical straw.
这条线变成了A child drinks a liquid of density ? through a vertical straw.所以请告诉我它们是如何保存在原形的。

下面是代码

   public void ReadMsWord()
    {
        // variable to store file path
        string filePath = null;
        // open dialog box to select file
        OpenFileDialog file = new OpenFileDialog();
        // dilog box title name
        file.Title = "Word File";
        // set initial directory of computer system
        file.InitialDirectory = "c:''";
        // set restore directory
        file.RestoreDirectory = true;
        // execute if block when dialog result box click ok button
        if (file.ShowDialog() == DialogResult.OK)
        {
            // store selected file path
            filePath = file.FileName.ToString();
        }
        Microsoft.Office.Interop.Word.Application word = new Microsoft.Office.Interop.Word.ApplicationClass();
        // create object of missing value
        object miss = System.Reflection.Missing.Value;
        // create object of selected file path
        object path = filePath;
        // set file path mode
        object readOnly = false;
        // open document                
        Microsoft.Office.Interop.Word.Document docs = word.Documents.Open(ref path, ref   
        miss, ref readOnly, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss,  
        ref miss, ref miss, ref miss, ref miss, ref miss, ref miss, ref miss);
        try
        {
            // create word application

            // select whole data from active window document
            docs.ActiveWindow.Selection.WholeStory();
            // handover the data to cllipboard
            docs.ActiveWindow.Selection.Copy();
            // clipboard create reference of idataobject interface which transfer the 
            data
            IDataObject data = Clipboard.GetDataObject();
            //set data into richtextbox control in text format
            string  t = "";
            string[] y = {};
            t = data.GetData(DataFormats.Text).ToString();
            string[] options = { };
            y = t.Split(''n');
           }
    catch(Exception ex)
    {
              throw ex;
    }
          }

t = data.GetData(DataFormats.UnicodeText).ToString();