I'm pretty sure that you need LiveCycle Workflow to use Quick Process Action Components (QPACs). I don't have this installed at the moment, but I think there is some documentation on using the Adobe provided QPACs either on the DVD image or in context help once it is installed.
You're completely correct that information on automating Reader Extensions is all the docs and not in a separate SDK, the Java API is explained in detail in those documents.
I only mentioned Workflow as the documentation for this product explains how to automate processes using QPACs, and so might be also useful for PrabuDass to check (if a Workflow licence is also available).
If no Workflow licence is available then as far as I'm aware Java is the only option. IIRC there used to be an example project floating around on the Adobe site which exposed Reader Extensions 7 as a web service and showed how to call it from .NET, but I can no longer locate it.