Represents the "ID" entry of the file trailer dictionary
It is defined as part of the PDF 1.1 specification.
It contains an array which contains strings, representing PDF
This string contains raw byte data. So it looks like a string
but really it is just a wrapper for data.
For definitive details see:.
The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 15,
The ISO PDF
Specification, ISO 32000-2:2017 PDF 2.0; Table: 15, page 58.