using (Image i = Image.FromFile(inputPath))
    {
    using (Graphics g = Graphics.FromImage(i))
        {
        g.DrawString("John", Font, Brushes.Black, new PointF(fX, fY1));
        g.DrawString("2018-10-01", Font, Brushes.Black, new PointF(fX, fY2));
        }
    i.Save(outputPath, ImageFormat.Png);
    }