using (var originalImage = Image.FromFile(@"d:\0\9\page01.PNG"))
            {
                var rectangleForCrop = new Rectangle(50, 50, 350, 350);
                using (var croppedImage = new Bitmap(rectangleForCrop.Width, rectangleForCrop.Height))
                {
                    using (var g = Graphics.FromImage(croppedImage))
                    {
                        g.DrawImageUnscaledAndClipped(originalImage, rectangleForCrop);
                    }
                    croppedImage.Save(@"d:\0\9\page01_cropped.png", ImageFormat.Png);
                }
            }