[pdf CYMK Export]

Hi, I'm looking for a way of doing the following:

I want to send a pdf of a project containing a vignette to a commercial printer. Here's the challenge:

1. creating a vignette (I can do this with layers with a gradient from black to transparent)
   
2. saving the picture as a pdf
   
3. here's the tricky part defining the black as CYMK 40 30 30 100 (not just a straight RGB to CYMK 0 0 0 100 mapping) to give a dark black when printed by a commercial printer
   

Photoshop express won't export pdfs

Paintshop won't either

Photoshop will, but is very very expensive

Will paint.net??

I attach a rough example to show what I mean.

Any suggestions welcome whether paint.net or other systems.