private async Task <byte[]> GetPDF(byte[] file, string id)
        {
            byte[] ret = null;

            string baseUrl = _configuration["baseUrl"];

            string inputFilename = @"wwwroot/pdf-template/cert.html";

            string imgsrc = $"data:image/png;base64,{QR.GetPureBase64($"{baseUrl}/Contract/Certificate?id={id}")}";

            HtmlDto dto = new HtmlDto()
            {
                html = System.Web.HttpUtility.HtmlEncode(
                    Encoding.UTF8.GetString(
                        System.IO.File.ReadAllBytes(inputFilename)))
                       .Replace("{certificateid}", id)
                       .Replace("{qrlink}", imgsrc),

                footerPath = $"{baseUrl}/pdf-template/footer.html"
            };

            string jsonString = Newtonsoft.Json.JsonConvert.SerializeObject(dto);

            string uri = _configuration["pdfApi"];

            var content = new StringContent(jsonString, Encoding.UTF8, "application/json");

            var response = await client.PostAsync($"{uri}", content).ConfigureAwait(false);

            var file2 = await response.Content.ReadAsByteArrayAsync();

            ret = Concat.DoConcat(file, file2);

            return(ret);
        }