DownloadUrlToBytes.cs

class Program
    {
        private static readonly HttpClient _httpClient = new HttpClient();

        static void Main(string[] args)
        {
            var url = "";
            byte[] fileBytes = null;

            var httpMessage = new HttpRequestMessage(HttpMethod.Get, url);
            var response = _httpClient.SendAsync(httpMessage).GetAwaiter().GetResult();

            using (var stream = response.Content.ReadAsStreamAsync().GetAwaiter().GetResult())
            using (var memStream = new MemoryStream())
            {
                stream.CopyTo(memStream);
                fileBytes = memStream.ToArray();
            }
        }
    }