The page scaling a print dialog starts with: the viewer preference PrintScaling.
public enum PdfPrintScaling
ISO 32000-2 §12.2, Table 147 (PDF 1.6). The default, and the value an unrecognized name reads as, is AppDefault.
kind:method, kind:property, kind:ctor. Press Esc to clear.AppDefaultThe viewer's default print scaling (AppDefault, the default).NoneNo page scaling (None).