//自适应尺寸
        private void adaptButton_Click(object sender, EventArgs e)
        {
            //获取屏幕的宽度和高度
            int w = Screen.PrimaryScreen.Bounds.Width;
            int h = Screen.PrimaryScreen.Bounds.Height;
            
            ddoc.pictureBox1.Location = new Point(0, 0);
            ddoc.pictureBox1.Size = new Size(w, h);

            ddoc.pictureBox1.SizeMode = PictureBoxSizeMode.Zoom;
        }

string strWelcome = System.Windows.Forms.Application.StartupPath + "\\welcome.jpg";
if (File.Exists(strWelcome))
{
    Bitmap bm = new Bitmap(Image.FromFile(strWelcome), ddoc.pictureBox1.Width, ddoc.pictureBox1.Height);
    bm.Save("filename");
}