Almost all Altium output I've seen, the PDF generates at an incorrect nonsense page dimension (e.g., 10.67 x 8.00"). Don't know offhand if this is different or configurable within the OutJob (I recall Smart PDF and OutJob outputs are subtly different), or if it's still around in Altium 15.
I normally tell it to print "fit to page", on the correct paper, and it works out OK (I think that should be slightly under scale, unfortunately, because the printer won't scale to net size, but to net size minus a small margin all around).
Tim