Represents the "UR" entry of the permissions dictionary object.

It is an optional entry defined as part of the PDF 1.5 specification. It was deprecated in PDF 2.0.

It contains a SignatureElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 258, page 477.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 263, page 589.