An application adapter is a plug-in that is loaded when an application is started. CCF passes control to the adapter whenever an operation is being performed. This gives you an opportunity to write custom code to modify how an application behaves. Another way to look at application adapters is that they give developers of hosted Web and hosted external applications much of the same capabilities that developers of hosted Windows Forms applications have.
An adapter is a managed code DLL, which is loaded at run time in the same way that hosted Windows Forms applications are loaded. However, adapters do not have a UI and are not visible to the user.