Gets or sets the annotation flags (F, PDF 1.1), every bit as stored; None when absent.
public PdfAnnotationFlags Flags { get; set; }
ISO 32000-2 §12.5.3, Table 167. A real number is truncated, and bits the table does not define are kept; both record a diagnostic. Text annotations behave as if NoZoom and NoRotate were set, whatever this says (§12.5.6.4).