Add-ons enable the user to extend an installed version of EPLAN. Using an add-on, you can basically distribute and centrally administer the following kind of date:
When the EPLAN version is started the first time after an add-on installation was done, the new add-on is registered automatically to this EPLAN version (When the add-on is set to autoregister).
Add-ons can be installed and updated automatically or manually, locally or from a server.
Every add-on can be registered as API dlls automatically. It is also possible to register a script when the add-on is registered.