Why does text/htm contenttype break scripts?

See more:

C#

ASP.NET

WebAPI

I have the following code:

[AcceptVerbs("GET")]
    [AllowAnonymous]
    [Route("ManageAccount/{id}")]
    public HttpResponseMessage ManageAccount(string id)
    {
        if (! String.IsNullOrEmpty(id))
        {

            var path = "C:/Users/user/Project/" + id + ".html";
            var response = new HttpResponseMessage();
            response.Content = new StringContent(File.ReadAllText(path));
            response.Content.Headers.ContentType = new MediaTypeHeaderValue("text/html");
            return response;
        }
        var path2 = "C:/Users/user/Project/Login.html";
        var response2 = new HttpResponseMessage();
        response2.Content = new StringContent(File.ReadAllText(path2));
        response2.Content.Headers.ContentType = new MediaTypeHeaderValue("text/html");
        return response2;
    }

I set ContentType to be text/html to read html page, but this page has scripts, now all scripts read as text/html !

What I have tried:

[AcceptVerbs("GET")]
    [AllowAnonymous]
    [Route("ManageAccount/{id}")]
    public HttpResponseMessage ManageAccount(string id)
    {
        if (! String.IsNullOrEmpty(id))
        {

            var path = "C:/Users/user/Project/" + id + ".html";
              var response = new HttpResponseMessage();
                response.Content = new StringContent(File.ReadAllText(path));
                response.Content.Headers.ContentType = new 
                MediaTypeHeaderValue("text/html");
              response.Headers.Add("Accept-Ranges", "bytes");
                return response;
        }
        var path2 = "C:/Users/user/Project/Login.html";
        var response2 = new HttpResponseMessage();
        response2.Content = new StringContent(File.ReadAllText(path2));
        response2.Content.Headers.ContentType = new MediaTypeHeaderValue("text/html");
        return response2;
    }

How can I fix this ????
Scripts from cdn work just fine but I need my scripts
I got that if scripts loaded in server it work !
So, what can I do?