I have tested the scenario using one of my sample PDF files and as per my observations, Page.PageInfo and PdfFileInfo instances are returning same Width and Height values. Furthermore, the page height and width properties use points as the basic unit, where 1 inch = 72 points and 1 cm = 1/2.54 inch = 0.3937 inch = 28.3 points.
I have tested the scenario and have observed that different page dimensions are being returned when using Document and PdfFileInfo instances. For
the sake of correction, I have logged it in our issue tracking system as PDFNEWNET-38870. We
will investigate this issue in details and will keep you updated on the status
of a correction.