PDF files are the most common form of soft proofing in the printing industry. You’ll want to be sure that you (and your customers!) are viewing color as accurately as possible when approving PDFs for print production. This means making sure the color is accurate and that you’re viewing exactly how inks (and objects!) will overprint when the ink hits the paper.
Acrobat and Reader both have an Overprint Preview preference that shows how inks will interact with each other on press. If the preview shows something that isn’t how the file should print, it gives you the opportunity to repair it before sending it off to your print service provider, or before the file is output. Overprint Preview is turned off by default (both in Acrobat and the free Adobe Reader) and must be activated in the preferences of each application. Select Acrobat (or Reader)>Preferences>General. Next, select Page Display from the list. In the Use Overprint Preview pull-down menu, choose Always.