Action<T> Delegate between 2 applications

Question

Hi,

 

I'm creating a C# dll which is going to be called from another c# application.

The dll task is to print documents. It will queue the requests & print the docs 1 after another.

I would like the c# dll, once it has printed a doc, to notify the calling application.

Then a message will be displayed on the user's screen.

Trying to achieve this using Action<T> Delegate but can't get it to work.

What's the correct usage of Action<T> Delegate in both the dll & main application in this example?

Thanks