Represents the "F" entry of the version 2.0 opi dictionary object.

It is a required entry defined as part of the PDF 1.0 specification.

It contains a FileSpecificationElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 370, page 641.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 407, page 825.

The F entry holds the file specification of the high-resolution image original, which may be a full dictionary with platform-specific paths and embedded file references.