private void Form1_Load(object sender, System.EventArgs e)
{
    // Initialize the DataGridView control.
    this.DataGridView1.ColumnCount = 5;
    this.DataGridView1.Rows.Add(new string[] { "A", "B", "C", "D", "E" });
    this.DataGridView1.Rows.Add(new string[] { "F", "G", "H", "I", "J" });
    this.DataGridView1.Rows.Add(new string[] { "K", "L", "M", "N", "O" });
    this.DataGridView1.Rows.Add(new string[] { "P", "Q", "R", "S", "T" });
    this.DataGridView1.Rows.Add(new string[] { "U", "V", "W", "X", "Y" });
    this.DataGridView1.AutoResizeColumns();
    this.DataGridView1.ClipboardCopyMode = 
        DataGridViewClipboardCopyMode.EnableWithoutHeaderText;
}

private void CopyPasteButton_Click(object sender, System.EventArgs e)
{
    if (this.DataGridView1
        .GetCellCount(DataGridViewElementStates.Selected) > 0)
    {
        try
        {
            // Add the selection to the clipboard.
            Clipboard.SetDataObject(
                this.DataGridView1.GetClipboardContent());
            
            // Replace the text box contents with the clipboard text.
            this.TextBox1.Text = Clipboard.GetText();
        }
        catch (System.Runtime.InteropServices.ExternalException)
        {
            this.TextBox1.Text = 
                "The Clipboard could not be accessed. Please try again.";
        }
    }
}