Setting zoom option at creation of pdf package

I'm using the programme to create pdf documents of images to preview to clients. Assembling the files into a pdf package I want the whole image to be viewed at fit to page so you can view the whole image. In my preferences this is the zoom option Iv'e set but when I create each pdf package the images are at various zoom levels and I can't figure out how to set fit to view as the zoom option when the package is created. Any help much appreciated.