The cpdf_page_init() function starts a new
page with height height and width
The page has number page_number and orientation
can be 0 for portrait and 1 for landscape. The last optional parameter
unit sets the unit for the coordinate system.
The value should be the number of postscript points per unit. Since
one inch is equal to 72 points, a value of 72 would set the unit
to one inch. The default is also 72.
See also cpdf_set_current_page().