internal class Program
    {
        private static void Main(string[] args)
        {
            using (var client = new HttpClient())
            using (var content = new MultipartFormDataContent())
            {
                // Make sure to change API address
                client.BaseAddress = new Uri("http://localhost:53798/");

                // Add first file content 
                var fileContent1 =
                    new ByteArrayContent(File.ReadAllBytes(@"C:\temp\file.zip"));
                fileContent1.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
                {
                    FileName = "test.zip"
                };

           

                content.Add(fileContent1);

                // Make a call to Web API
                content.Headers.Add("encryptedPassword", "haslo123123");
                content.Headers.Add("imei", "123");
                content.Headers.Add("pseudoUdid", "1");
                content.Headers.Add("versionCode", "1");
                var result = client.PostAsync("http://api.idcopy.hostingasp.pl/api/document/post", content).Result;

                System.Console.ReadLine();
            }
        }
    }