private void wrapHtml()
{
 string textboxData = string.Empty; 
            string selectedText = string.Empty; 
            string htmlTagOpen = ""; 
            string htmlTagClosed = ""; 

            textboxData = textBox1.Text; 
            selectedText = textBox1.SelectedText; 
            textBox1.Text = textboxData.Replace(selectedText, htmlTagOpen + selectedText + htmlTagClosed);
}