我的代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Wordprocessing;

namespace WordDocManipulation
{
    class Program
    {
        static void Main(string[] args)
        {

            string path = @"C:\sample.docx";
            string strtxt = "Hello This is done by programmatically";      

           OpenAndAddTextToWordDocument(path,strtxt);
        }
        public static void OpenAndAddTextToWordDocument(string filepath,string txt)
        {
            /* I want to the below text to be added in the new section */ 

            // Open a WordprocessingDocument for editing using the filepath.
            WordprocessingDocument wordprocessingDocument =
                WordprocessingDocument.Open(filepath,true);

            // Assign a reference to the existing document body.
            Body body = wordprocessingDocument.MainDocumentPart.Document.Body;

            // Add new text.
            Paragraph para = body.AppendChild(new Paragraph());
            Run run = para.AppendChild(new Run());
            run.AppendChild(new Text(txt));

            // Close the handle explicitly.
            wordprocessingDocument.Close();
        }
    }
}

我该怎么办？