after or before printing to the PDF Printer?
There are a couple of different methods that can be used to execute an application either after of before the printing process has started. However I believe the easiest solution is to trap the events fired by the PDF Converter and depending on the event fired, process your application.
Each time any output is sent to the PDF Converter, the EnabledPre() event is fired. If you handle this event, your will know that output has be sent to the Printer and you can consequently execute your other application. On the other side, when the ENDDOCPOST() event is fired you are sure the printing process is terminated and you can process you other application. You can find a detailed explanation about this process on pages "147" and "148" of the "Common Driver Interface210.pdf" that is shipped with the product.