Under Edit > Preferences there is a section called "Page Display". My Adobe Reader is set by default to Custom Resolution 110 pixel/inch. There is another option next to it that says use system resolution 96 pixel/inch.Is Adobe Reader always set by default to 110 pixel/inch? Because on my friend's older computer I noticed he had 96 ppi selected by default, but on the newer computers of other friends I noticed 110ppi was the standard.
The reason I ask is that I want to save the pictures I include in my PDF portfolio at the most common ppi. So if 90% of people have their reader set to 110 I want to crop my pictures to 110. But if its divided half and half between 110 and 96 it might be better to compromise and crop the pictures at 100ppi for example.