From Xojo Documentation
Displays the standard Page Setup dialog box.
If the SetupString property has been populated before this method is called, the Page Setup dialog box will reflect the settings stored in the SetupString property. After the user clicks the OK button to close the Page Setup dialog box, all of the PrinterSetup properties will be updated to reflect the settings the user chose.
On a macOS, PageSetupDialog takes an optional parameter, window. If specified, the Page Setup dialog will appear as a sheet connected to that window.
This example displays the Page Setup dialog box and then stores the settings the user chose in a variable: