Represents the "F" entry of the user property dictionary object.

It is an optional entry defined as part of the PDF 1.0 specification.

It contains a string representing a PDF string object.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 329, page 569.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 362, page 737.

The F entry holds a formatted text string for displaying the property value to users, allowing an application to control display without requiring the viewer to implement its own formatting.