Region
Key point: Select a specific area in an image or PDF document to add a URL, xref or comment.

In images and PDF documents, you can draw a region and add a URL, an xref, or a comment on the region.

Click the image or PDF and then click the icon in the document toolbar to show existing regions.

With this feature, you can connect parts of images or PDF documents to other documents, including other PDF documents, or even to external resources.

Also see How to add a region to a PDF or an image.