private void button3_Click(object sender, EventArgs e)
    {
        if (this.Font.Style != FontStyle.Bold)
        {
            this.Font = new Font(this.Font, FontStyle.Bold);
        }
        else if (this.Font.Style != FontStyle.Italic)
        {
            this.Font = new Font(this.Font, FontStyle.Italic);
        }
        else if (this.Font.Style != FontStyle.Underline)
        {
            this.Font = new Font(this.Font, FontStyle.Underline);
        }
        else
        {
            this.Font = new Font(this.Font, FontStyle.Regular);
        }

    }