public ActionResult GetPdf() {
    //Create a new document
    PdfDocument doc = new PdfDocument();

    //Create a new render
    AcmRender render = new AcmRender(doc);

    //Create some contents
    AcmContent content = new AcmContent(new AcmText("Hello!"));

    //Render the content
    render.Render(content);

    //Instead of saving the document to a local file, here it 
    //saves the document to output stream of the current
    //HttpResponse object. It also set the content type as
    //"application/pdf"
    HttpResponse response = HttpContext.Current.Response;
    response.Clear();
    response.ClearHeaders();
    response.ContentType = "application/pdf";
    doc.Save(response.OutputStream);

    return File.....() // what???
}