netframework转core时文件响应流问题

    /// <summary>
        /// 根据pdf的预览id获取预览的pdf
        /// </summary>
        /// <param name="Id"></param>
        /// <returns></returns>
        [HttpGet]
        [Route("GetPreviewPdf")]
        public HttpResponseMessage GetPreviewPdf(Guid Id)
        {
            string pdfBase64String = _cacheManager.Get<string>(Id.ToString());
            var response = new HttpResponseMessage();
            if (!string.IsNullOrEmpty(pdfBase64String))
            {
                byte[] pdfArray = Convert.FromBase64String(pdfBase64String);

                response.StatusCode = System.Net.HttpStatusCode.OK;
                response.Content = new ByteArrayContent(pdfArray);
                response.Content.Headers.ContentType = MediaTypeHeaderValue.Parse(MimeTypes.ApplicationPdf);
            }
            else
            {
                response.StatusCode = System.Net.HttpStatusCode.Gone;
            }
            return response;

        }

      public IServiceProvider ConfigureServices(IServiceCollection services)
        {
            services.AddMvc().AddWebApiConventions();
}