Stream stream = App.GetResourceStream(new Uri("Resources/" + Path.GetFileName(fileName), UriKind.Relative)).Stream;
using (FileStream fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write))
{
    byte[] bytes = new byte[stream.Length];
    stream.Read(bytes, 0, bytes.Length);
    fileStream.Write(bytes, 0, bytes.Length);
}