Represents the "FS" entry of the file attachment annotation 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: 184, page 406.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 187, page 492.

The file specification references the embedded file. The embedded file's data is stored in an EmbeddedFiles name tree entry or directly in a stream object within the PDF.