如何删除Word文档中的符号

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;
                }
            }
        }