Plug-In Model

[Srikanth]

Hi all,

Can any one give details about plug-in models in .NET?

We have an application which will consists of a different documents, which
will be displayed in 2 different tree views based on the type of document.
and now we are dispatching to our clients. One of clients requires an
additional document which is not necessary for others. So we need to
implement the plug-in model which will extend the features of such
documents. Means the plug-in willl consist the extra document implementation
which is required by the client and will be dispatched to that client. The
plug-in can interact with our core framework.

Basically our document base class consists the following

public class DocumentBase
{
string name;
DocumentInfo Info;
}

and we have even

public class DocumentCollect ionBase : CollectionBase
{
//Which will have a collection of DocumentBase
}
Now i need to have plug-in which will have an extra document named
"DeclineDocumen t" which will extend the features from the document base. And
i need to load the documents from the plug-in code and i need to display
them in the user interface along with the documents available with the core
framework.

I can have any number of such plug-ins.

Are there any design patterns for the PlugIns in MSDN?
Any sample applications will be helpful.

Thanks In Advance
-Srikanth