Represents the "Length" entry of the stream object.
It is a required entry defined as part of the PDF 1.0
It contains an integer representing a PDF numeric object.
It describes the number of bytes of data in the stream.
For definitive details see:.
The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 5, page
The ISO PDF
Specification, ISO 32000-2:2017 PDF 2.0; Table: 5, page 32.