You can donwload our API Reference from here.
Unzip the archive and run index.html.
If you want to use the search functionality you should copy the unzipped "HelpOutput" folder to C:\inetpub\wwwroot on your machine. After that start the browser and navigate to http://localhost/helpoutput/index.aspx
Note: If you can't find C:\inetpub\wwwroot you should enable Internet Information Services (IIS).