What is an OCG?

An OCG (Optional Content Group), defined in ISO 32000-2:2020, clause 8.11, is a PDF feature that enables selectable layers in interactive PDF viewers.

OCGs allow users to toggle the visibility of specific content, such as text, images, or annotations, within a PDF. Commonly used for technical drawings, multilingual documents, or layered graphics, OCGs enhance interactivity and customization in PDF presentations.