In most report with large page number, it's recommended to use page numbering on top or bottom of the page. ClientUI scripting have provided some mechanisms to retrieve the current page number and total page. To learn about scripting, see ClientUI Scripting Overview.
To simplify report creation, ClientUI Report Designer provides a shortcut to easily insert page numbers into a report, which can be accessed from the ribbon bar. You also can customize the page number format, and it's position. See the following illustration.