There are two kinds of rotation in PDF documents - a viewing rotation which can be set, making a PDF viewer such as Acrobat Reader open the docment with its pages appearing to be rotated by 90, 180 or 270 degrees, and the actual rotation which is how the text and graphics on a page are layed out (portrait or landscape).
The cpdflib functions Rotate and RotateBy set or alter
the viewing rotation, and the function RotateContents alters the actual
rotation. The function Upright changes the viewing rotation to 0 and, if
necessary counterrotates the actual rotation to compensate. This is useful
because many cpdflib functions require upright pages to work as
expected.