How do I support drag-and-drop for a RichTextBox?

You must set the ‘AllowDrop’ property on the RichTextBox control to true and also handle both the ‘DragEnter’ and ‘DragDrop’ events.

Add event handlers to the control as given below.

[C#]

using System.Windows.Forms;
richTextBox1.DragEnter += new DragEventHandler( richTextBox1_DragEnter );
richTextBox1.DragDrop += new DragEventHandler( richTextBox1_DragDrop );

Write event handlers :
{
        private void richTextBox1_DragEnter(object sender, DragEventArgs e)
        {
            e.Effect = e.Data.GetDataPresent(DataFormats.Text)
              ? DragDropEffects.Copy
              : DragDropEffects.None;
        }

        private void richTextBox1_DragDrop(object sender, DragEventArgs e)
        {
            // Load the file into the control
            string text = (string)e.Data.GetData('Text');
            richTextBox1.LoadFile(text, RichTextBoxStreamType.RichText);
        }

        public Window1()
        {
            InitializeComponent();
        }
    }