Return a PDF to the browser in the form of a byte array.

FileServiceController.cs

using System.IO;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Web.Http;

public class FileServiceController : ApiController
{
        [Route("api/fileservice/{docId}")]
        public HttpResponseMessage Get(string docId)
        {
            byte[] response = FileProxy.GetDocumentStream(docId);

            if (response == null) return new HttpResponseMessage(HttpStatusCode.BadRequest);

            MemoryStream ms = new MemoryStream(response);
            HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
            result.Content = new ByteArrayContent(ms.ToArray());
            result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
            return result;
        }
}