This is a setting in Acrobat that when set properly helps you to see how inks will overprint when they are printed on paper. This setting can be changed in both Acrobat Professional and Reader. Below is an example of what differences you would see with the setting off or on. The image on the right is how your job would print. The one on the left is how your file could look on your screen if you do not have this feature activated.

To turn this feature on, go to your Preferences or Properties and change “Use Overprint Preview” to “Always”. See below: