Overprint is primarily used to intentionally overlap inks for a number of reasons. It can cause unexpected results. We suggest that you turn all overprint objects off before submitting your files. Overprinting a color can result in the interactions of two inks (colors), producing unexpected results. When overprint is set on a white object, it simply causes it not to show at all. One of the problems is you will not necessarily be able to tell on your computer screen.