I need to save a PDF at 50%

I have a 12 inch brochure I want to print at 6 inch, how can I save the pdf from indesign at 50% so they print it right? There is no option for it anywhere, thought it would be in general..I guess I could do a ps file and then distil it but there must be a better way

if anyone knows, I'm in a bit of a bind...thanks