I am trying to design a billboard, and I cannot save this document as a PDF to submit it for approval. What format should I build this in and what program is the best, photoshop or illustrator?

Are you saying you CAN'T save it as a PDF or that your client won't accept one as a proof? If you can't save it as such, why not?

In any case, I'd suggest that the right software would depend on what the billboard will feature. If it will show raster images, like photographs, then you'll probably want to go with Photoshop. If it will consist strictly of line art and shapes, you'll be better off with Illustrator. If it will contain a combination of the two, perhaps you could place the raster art from Photoshop into an Illustrator file. I've never set up a file for a billboard before, but these suggestions stand as generalities.

You'll be better off if you get specs from whomever will be doing the printing. Give them a call and they should be able to tell you exactly what they'll need. If you're producing a raster image a billboard will probably require a fairly low resolution, so ask about that too. Good luck.

Talk to the art department of the company who will be printing it. They will be your best source for formatting info specific to the way they do things.

I used to design and print billboards, and I'm gonna go out on a limb and guess that you're trying to build a file at WAY too huge a resolution setting, just for starters.

I have designed this document in photoshop and it will not allow me save it in pdf format. I have tried many different ways and i'm stumped at what to do next. I will contact the company and maybe they can give me the right answer. Thanks

What version of PS.
What are the document specs.
What error do you get when saving as pdf.
Why pdf for a one page image file?

Ed