A graphics question for all you artists out there.

How do you preserve the layers when saving as a pdf from Photoshop?

I know how to save as pdf but I have many layers I want to turn on / off when printing from the pdf but I can't find how to keep the multiple layers.

Either my search criteria is useless or I'm thicker than a blue whale's tongue as all my searches show "how to save as a pdf" which I know how but it flattens the image and doesn't preserve the layers.

Can anyone point me in the right direction?

Photoshop CS5

I know I've read a thread on PDF layers in another forum, but I don't know if posting the link would be OK.

Here it is:

Hope I'm not breaking the rules.

I saw what looked like a straight-forward explanation of how to do multi-layered pdf files by passing the Photoshop file through Illustrator. If you have Illustrator, I can try to dig up the link I'm remembering.