One rectangle of pixels of one page at one zoom: what a DocumentSession renders and hands to an IRenderSurface.
public Tile(int PageIndex, double Scale, PixelRectangle Region)
The zero-based page.
The pixels, in the coordinates of a render of the whole page at Scale and Rotation: origin at the
top-left corner of the rotated crop box, y down (GetPixelRectangle(PdfPage)).
ISO 32000-2 §8.3.2.2 (device space) and §14.11.2 (the crop box is the region displayed). Spec #33 story 54 (viewer capability 1). A tile's pixels equal the same pixels of a whole-page render (to one level at the last bit of the transform, see Region), so a mosaic of tiles shows no seams.