Global.asax.cs

 public class WebApiApplication : System.Web.HttpApplication {
    [ImportMany]
    List<IComposableApiMetadata> m_composers;
    private CompositionContainer m_container;

    protected void Application_Start() {

     
      var catalog = new AggregateCatalog();
      var servicesFolder = @"C:\dllFolder";
      catalog.Catalogs.Add(new DirectoryCatalog(servicesFolder));

      m_container = new CompositionContainer(catalog);
      m_container.ComposeParts(this);

      var builder = new ContainerBuilder();


      foreach (var composableApiMetadata in m_composers) {
        composableApiMetadata.Compose(builder);
        builder.RegisterApiControllers(composableApiMetadata.ApiAssembly());
      }

      var container = builder.Build();

      var resolver = new AutofacWebApiDependencyResolver(container);

      GlobalConfiguration.Configuration.DependencyResolver = resolver;

      AreaRegistration.RegisterAllAreas();
      WebApiConfig.Register(GlobalConfiguration.Configuration);
      FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
      RouteConfig.RegisterRoutes(RouteTable.Routes);
      BundleConfig.RegisterBundles(BundleTable.Bundles);

    }
  }