using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            var allFiles = Directory.GetFiles(textBox1.Text, "*.DTX", SearchOption.AllDirectories);
            foreach (var file in allFiles )
            {
                listBox1.Items.Add(file);
            }
            foreach (var file in allFiles)
            {
                listBox1.SetSelected(0, true);
                textBox2.Text = Path.GetFileName(file);
                File.Delete(file);
                System.IO.File.Copy(textBox3.Text, file);
                listBox1.Items.Remove(listBox1.SelectedItem);
            }
        }
    }
}