This documentation is not using the current rendering mechanism and is probably outdated. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
GetPageNumberAliasViewHelper / GetTotalNumberOfPagesAliasViewHelper¶
These ViewHelpers return alias strings to the current page number as well as the total number of pages. Please note that they do not return an integer value, but a string that is replaced by the correct number at the end of the PDF generation. This may lead to alignment errors when trying to align text including these ViewHelpers right or centered.