Integrating with Dynamics

I am new to Dynamics and I have a question. I have a webservice from another application that stores our invoices. What we would like is a way to open an invoice in Dynamics and then have some way to click on that invoice and have it open up the invoice from the third party application. The webservice can return whatever we need it to return.

How do I best approach this? Pass the invoice number on to the web service and have it return a path to a PDF? How do I then open up the PDF in Dynamics? Is there an easy way to tell Dynamics about the web service and have this happen easier?

What exactly are you trying to achieve,

Open a Invoice in PDF format on a Client PC using web service.