In this example, using the Bitmap class included in the System.Drawing namespace, an .ico file is converted to a .bmp file to display it in a PictureBox.

This is necessary because the .ico format is not supported by the PictureBox control.
C#

using System.Drawing;
using System.Windows.Forms;
  
namespace WindowsFormsApplication1
{
  public partial class Form1 : Form
  {
    public Bitmap FromIconToBitmap(Icon icon)
    {
      Bitmap bmp = new Bitmap(icon.Width, icon.Height);
      using (Graphics gp = Graphics.FromImage(bmp))
      {
        gp.Clear(Color.Transparent);
        gp.DrawIcon(icon, new Rectangle(0, 0, icon.Width, icon.Height));
      }
      return bmp;
    }
  
    private void Button1_Click(System.Object sender, System.EventArgs e)
    {
      Icon icon = WindowsFormsApplication1.Properties.Resources.Icon1;
      pictureBox1.Image = FromIconToBitmap(icon);
    }
  }
}