In order to use the Denodo4E plugin to develop a Denodo custom extension, a Denodo Platform Server must be installed in the local machine. Because, the libraries that the plugins depends on are only included in the Denodo Platform Server installation, not on the client installation.
For more information, refer to the [Installing Denodo4E Plugin](https://community.denodo.com/docs/html/browse/8.0/denodo4e/install_denodo4e/install_denodo4e#installing-denodo4e) section of the Denodo 4Eclipse Guide.
In order to obtain a complete installation on the local machine, you can either install the [Denodo Express](https://community.denodo.com/express/download) or request a Denodo installer and a license to the Denodo Platform Server Administrator.
But with the Denodo Express installation, you can develop and debug any type of custom extensions expect the VDP custom wrapper. However you can only develop VDP custom wrapper but not debug them using the Denodo4E Plugin. In this case, I would recommend you to refer to the knowledge base article [How to debug Denodo Custom Extensions with Eclipse](https://community.denodo.com/kb/view/document/How%20to%20debug%20Denodo%20custom%20extensions%20with%20Eclipse?category=Custom+Elements) without using the Denodo4E plugin.
Hope this helps!