Represents the "Extensions" entry of the catalog dictionary object.

It is an optional entry defined as part of the PDF 1.0 specification.

It contains an ExtensionsElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 28, page 73.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 3.25, page 23.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 29, page 98.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 242, page 458.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 245, page 555.

The Extensions entry references the Extensions dictionary, which lists all developer extensions the document uses. Each extension is identified by a prefix name, a base PDF version, and an extension level number.