How to Convert .DOC to .TXT file?

private string ReadDocFile(object sPath, ref string sDocContent)
{
    Microsoft.Office.Interop.Word.ApplicationClass wordApp = new Microsoft.Office.Interop.Word.ApplicationClass();
    object missing = System.Reflection.Missing.Value;
    Word._Document aDoc = null;
    aDoc = wordApp.Documents.Open(ref sPath, 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);
    aDoc.Activate();
    aDoc.ActiveWindow.Selection.WholeStory();
    aDoc.ActiveWindow.Selection.Copy();
    IDataObject data = Clipboard.GetDataObject();
    sDocContent = data.GetData(DataFormats.UnicodeText).ToString();
    wordApp.Documents.Close(ref isNoSave, ref missing, ref missing); ;
    wordApp.Quit(ref isNoSave, ref missing, ref missing);
    return (string)sDocContent;
}