Download selected pdf files from a datatable

my controller looks like

[HttpPost]
    public FileResult methodname(string files)
    {
        String CurrentDate = DateTime.Now.Date.ToString("dd-MM-yyyy");
        string dir = filepath + "/" + CurrentDate + "/";
        string[] fileList = files.Split(",");
        var count = fileList.Length;
        try
        {
            _log.LogInformation("Enter Action with user name " + HttpContext.Session.GetString("UserName"));
            using (var memoryStream = new MemoryStream())
            {
                using (var ziparchive = new ZipArchive(memoryStream, ZipArchiveMode.Create, true))
                {
                    for (int i = 0; i < count; i++)
                    {
                        ziparchive.CreateEntryFromFile(dir + fileList[i], fileList[i]);
                    }
                }
                return File(memoryStream.ToArray(), "application/zip", "Attachments.zip");

            }
        }
        catch (Exception ex)
        {
            _log.LogError(ex.StackTrace);
            return null;
        }

    }