Expanding Automator's library of actions is easy. Actions installed in third-party applications automatically appear in the Automator library view. In addition, you can add new actions yourself by selecting Import Actions... from Automator's File menu and selecting the action files you've received from trusted sources. After all, the more actions you have, the more you can automate.
Automator and Security
Automator actions are very powerful. It's very important to apply the same security safeguards to using Automator actions as you would with applications or other items downloaded from the Internet or received from third parties. Only install actions from trusted sources.