I too woud like to know how to do this. We have our page numbers working fine on PDFs generated on FMP12 but the scripts don't work on Filemaker Go due to lack of preview mode. Any help would be greatly appreciated!
The methods that work in FileMaker Pro for this don't work in GO as you can't enter preview mode in Go.
If you do not have any objects set to "slide up/resize enclosing part", then it is, in theory, possible to use the total number of records in your found set to compute the total pages. If you have sub summary layout parts it's more complicated as you then have to count the number of record groups, but is still possible to do.