All visible steps have an Overprint Black option. Overprint black is mostly useful in creating CMYK PDFs for long run printers. However, it has a few side effects you should know about.
When overprint black is set to yes, the step will:
- Disable all color fields and assume they are set to black.
- Place all overprint black items on top of all non-overprint black items.
- Convert images to grey scale.
For more information on how overprint black works in CMYK PDFs, watch this video: