Получение иконки приложения по расширению.

      В данном примере мы рассмотрим получение иконки приложения из любого файла. Мы получаем иконку программы по умолчанию открывающей данный тип файла.
Вам необходимо будет подключить библиотеки:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
using System.Drawing;
using System.IO;
using System.Runtime.InteropServices;
using System.Windows.Media.Imaging;

[StructLayout(LayoutKind.Sequential)]
public struct SHFILEINFO
{
    public IntPtr hIcon;
    public IntPtr iIcon;
    public uint dwAttributes;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
    public string szDisplayName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
    public string szTypeName;
};

private class Win32
{
    public const uint SHGFI_ICON = 0x100;
    public const uint SHGFI_LARGEICON = 0x0;
    public const uint SHGFI_SMALLICON = 0x1;

    [DllImport("shell32.dll")]
    public static extern IntPtr SHGetFileInfo(string pszPath, uint dwFileAttributes, ref SHFILEINFO psfi, uint cbSizeFileInfo, uint uFlags);
}

public static BitmapImage GetImageBitmapImage(string filename)
{
    try
    {
        SHFILEINFO shinfo = new SHFILEINFO();
        IntPtr ptr = Win32.SHGetFileInfo(filename, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), Win32.SHGFI_ICON | Win32.SHGFI_SMALLICON);
        Icon icon = Icon.FromHandle(shinfo.hIcon);

        MemoryStream ms = new MemoryStream();
        icon.Save(ms);
        ms.Position = 0;

        BitmapImage bi = new BitmapImage();
        bi.BeginInit();
        bi.StreamSource = ms;
        bi.EndInit();

        return bi;
    }
    catch
    {
        return null;
    }
}

public static Icon GetImageIcon(string filename)
{
    try
    {
        SHFILEINFO shinfo = new SHFILEINFO();
        IntPtr ptr = Win32.SHGetFileInfo(filename, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), Win32.SHGFI_ICON | Win32.SHGFI_SMALLICON);
        Icon icon = Icon.FromHandle(shinfo.hIcon);

        return icon;
    }
    catch
    {
        return null;
    }
}

private Bitmap BitmapImage2Bitmap(BitmapImage bitmapImage)
{
    using (MemoryStream outStream = new MemoryStream())
    {
        BitmapEncoder enc = new BmpBitmapEncoder();
        enc.Frames.Add(BitmapFrame.Create(bitmapImage));
        enc.Save(outStream);
        System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(outStream);        
        return new Bitmap(bitmap);
    }
}

private void button1_Click(object sender, EventArgs e)
{
    Icon a = GetImageIcon(@"C:\Windows\explorer.exe");
    Image im = a.ToBitmap();
    pictureBox1.Image = im;

    BitmapImage b = GetImageBitmapImage(@"C:\Windows\explorer.exe");
    Image i = BitmapImage2Bitmap(b);
    pictureBox2.Image = i;     
}