If that's the case then there's a need to know the pdf creator software that your programmer will use, advise him/her to get to the specific dpi you want.
dpi of images are not that important to be huge, since .pdf has built-in resolution fixer for images, it's not a big deal.
setting it up as 300dpi will make your .pdf bloated and will usually hang on load time.
setting it up like 72dpi is the set standard