If you route your assignment, using the standard flow-route-feature, does it send email and attach the email much like you want to do?

If so, trace it with the Pega tracer to see how it does it.  (That's what I might do, since I can never remember what the rules are that actually to the emailing)

Sorry, I don't know the difference between a "mail correspondence" and an email.   However, it sounds like you have general parts, the first being to generate some kind of data object, and the second being to attach the object to the work.

For that second part, of attaching the object to the work, you can trace the smart-pdf flow shape so you can see how it attaches the pdf to the work, since even though your object is not a pdf, the attach mechanism will be the same.