Download file using WCF Rest service?

A sample method i use to download the file from my REST service:

[WebGet(UriTemplate = "file/{id}")]
        public Stream GetPdfFile(string id)
        {
            WebOperationContext.Current.OutgoingResponse.ContentType = "application/txt";
            FileStream f = new FileStream("C:\\Test.txt", FileMode.Open);
            int length = (int)f.Length;
            WebOperationContext.Current.OutgoingResponse.ContentLength = length;
            byte[] buffer = new byte[length];
            int sum = 0;
            int count;
            while((count = f.Read(buffer, sum , length - sum)) > 0 )
            {
                sum += count;
            }
            f.Close();
            return new MemoryStream(buffer); 
        }