Insert the JPEG in your drawing on a specific layer. And when you make PDF make sure to set the layer to ON. Once PDF is done then you may set the layer to off. You can also insert JPEG in active drawing, make PDF and then delete the JPEG. Both of these are what you can do manually.
Both the above tasks can be done via a macro (I'll look into that little later).
I want this task via macro.
I am waiting...