如何删除word文档中的符号

我正在使用wordapi（c#2.0应用程序）通过程序将word文档转换为纯文本文件。对于某些文档，由于单词document中的符号可用，该过程处于挂起状态。我想用程序删除word文档中的那些符号，或者如何将word文档保存到包含符号的纯文本文件中而不挂起。

请帮我解决的问题

这是示例代码

private void TextFileConvertion(string strsource, string strtarget)
        {
            // Use for the parameter whose type are not known or  
            // say Missing
            object Unknown = Type.Missing;
            //Creating the instance of Word Application
            Word.Application newApp = new Word.Application();
            newApp.AutomationSecurity = Microsoft.Office.Core.MsoAutomationSecurity.msoAutomationSecurityForceDisable;
            newApp.DisplayAlerts = Word.WdAlertLevel.wdAlertsNone;
            Word.Document doc = null;
            try
            {
                lblProgress.Text = "Converting " + strsource + " into Text file is under process.";
                Application.DoEvents();
                // specifying the Source & Target file names
                object Source = strsource;
                object Target = strtarget;
                object objTrue = true;
                object objFalse = false;
                // Source document open here
                // Additional Parameters are not known so that are  
                // set as a missing type
                try
                {
                    newApp.Visible = false;
                    doc = newApp.Documents.Open(ref Source,
                         ref Unknown, ref Unknown, ref Unknown,
                         ref Unknown, ref Unknown, ref Unknown,
                         ref Unknown, ref Unknown, ref Unknown,
                         ref Unknown, ref Unknown, ref Unknown,
                         ref Unknown, ref Unknown, ref Unknown);
                }
                catch (Exception exp)
                {
                    ZoniacLogger.Error("Exception : " + exp.Message + " Stack Trace : " + exp.StackTrace);
                }
                if (doc.ReadOnlyRecommended == true)
                    return;
                // Specifying the format in which you want the output file 
                object format = Word.WdSaveFormat.wdFormatText;
                //Changing the format of the document
                newApp.ActiveDocument.SaveAs(ref Target, ref format,
                        ref Unknown, ref Unknown, ref Unknown,
                        ref Unknown, ref Unknown, ref Unknown,
                        ref Unknown, ref Unknown, ref Unknown,
                        ref Unknown, ref Unknown, ref Unknown,
                        ref Unknown, ref Unknown);
                //if (doc.ReadOnlyRecommended == true)
                //    SetuncheckReadonly(doc, strsource);
                //intTxtCounter = intTxtCounter + 1;
                strTxtCounter = "OK";
            }
            catch (Exception ex)
            {
                strTxtCounter = "FAILED";
                ZoniacLogger.Error("<TextFileConvertion> Exception : " + ex.Message + " Stack Trace : " + ex.StackTrace);
            }
            finally
            {
                if (newApp != null)
                {
                    // for closing the application
                    newApp.Quit(ref Unknown, ref Unknown, ref Unknown);
                    newApp = null;
                }
            }
        }