How can I add .htm at the end of URL in when using attribute routing in MVC 5

Question

 [Route("{page?}/{category?}/{detail?}")]
    public ActionResult Index(string page, string category, string detail)
    {
        navigation _nav = nav.GetItemByALias(MODULE_CODE, page, "vn");
        ViewBag.template = _nav.template_code;
        ViewBag.page = page;
        ViewBag.category = category;
        ViewBag.detail = detail;
        ViewBag.lang = "vn";
        if(_nav.template_code == "goldencity_news" && detail  != null && detail != "")
        {
            ViewBag.template = _nav.template_code + "_detail";
        }

        return View();
    }

Normally.

• local:port
• local:port/home
• local:port/page/category
• local:port/page/category/detail

All above is right

But, when I change (add .htm at Route config)

 [Route("{page?}/{category?}/{detail?}.htm")]
    public ActionResult Index(string page, string category, string detail)
    {
        navigation _nav = nav.GetItemByALias(MODULE_CODE, page, "vn");
        ViewBag.template = _nav.template_code;
        ViewBag.page = page;
        ViewBag.category = category;
        ViewBag.detail = detail;
        ViewBag.lang = "vn";
        if(_nav.template_code == "goldencity_news" && detail  != null && detail != "")
        {
            ViewBag.template = _nav.template_code + "_detail";
        }

        return View();
    }

only one case right:

• local:port/page/category/detail.htm.

This list below I need:

• Local:port
• Local:port/page
• Local:port/page.htm
• local:port/page/category
• local:port/page/category.htm
• local:port/page/category/detail
• local:port/page/category/detail.htm