The geometry of one page as a viewer lays it out: its crop box, rotation and user unit, cached by the session.
public PageMetrics(int Index, PdfRectangle CropBox, int Rotation, double UserUnit)
The zero-based page.
The crop box, in default user space (ISO 32000-2 §14.11.2): the region displayed.
The page's rotation in degrees clockwise: 0, 90, 180 or 270 (ISO 32000-2 §7.7.3.3, Rotate).
The size of a default user space unit in points (ISO 32000-2 §14.11.2, UserUnit).
ISO 32000-2 §7.7.3.3 and §14.11.2. Spec #33 story 54.