2.  在界面上拖放一个文本框（TextBox）

3.  双击窗体写窗体的加载事件，如下：

    private void mainForm_Load(object sender, EventArgs e)

    {

       this.textbox1.Multiline = true;//多行显示

       this.textbox1.AllowDrop = true;//允许用户拖拽数据到上面

       this.textbox1.ScrollBars = ScrollBars.Vertical;  //垂直上面显示滚动条     

    }

4.  写textbox1的DragEnter事件，如下：

    private void textBox1_DragEnter(object sender, DragEventArgs e)

    {

       //if (e.Data.GetDataPresent(DataFormats.FileDrop))

       //{

       //    string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);

       //    foreach (var file in files)

       //    {

       //        this.textBox1.AppendText(file);

       //    }

       //}

       if (e.Data.GetDataPresent(DataFormats.FileDrop))

       {

           string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);

           foreach (var file in files)

           {

              FileStream fs=new FileStream(file,FileMode.Open);

              StreamReader stream = new StreamReader(fs,Encoding.Default);

              string str = stream.ReadToEnd();

              this.textbox1.AppendText(str);

              stream.Close();

              fs.Close();             

           }

       }

    }