In Dynamics NAV 2013 R2 it is now possible, again, to implement Page X of Y for document reports.
In previous versions of RDLC the problem was that in a typical document report the content of the body was put in a List container to implement the Number Of Copies option. Via the List we then grouped the Body on the OutputNo variable. To be able to calculate the page number we then had to use complex expressions because of the fact that we had to reset it for every new copy. And there was no solution to calculate and reset the total pages.