In Visual Studio 2013 ASP.NET projects you can easily mix WebForms with MVC, WebAPI (Nondiscoverable REST via MVC) SPA and Facebook content. Read more…
This post just compares the default content.
1) WebForms 2) MVC and WebForms 3) MVC and WebAPI
In case 2) WebForms was selected as content and references added to MVC.
If the opposite is done like selecting MVC as content and add references to WebForms then the project becomes like 3)
If you want to enable MVC in an old WebForms project, then create a new project as case 2) and move your content to that project.