Gets or sets the trim box: the intended dimensions of the finished page after trimming.
public PdfRectangle TrimBox { get; set; }
ISO 32000-2 §7.7.3.3, Table 31, and §14.11.2. Defaults to the crop box; reduced to its intersection with the media box. Setting writes the entry as given (reading reduces it again) and records PDF 1.3 (Table 31). A mutation.