Hi Alfredo,
Please check below documentation for reference:
https://ej2.syncfusion.com/documentation/document-editor/section-format/#page-size
If you were using Documenteditor container, please use below code snippet to get page width and height( which is in points):
let pageWidth=container.documentEditor.selection.sectionFormat.pageWidth;
let pageHeight=container.documentEditor.selection.sectionFormat.pageHeight
Please let us know if you need any further assistance.
Regards,
Suriya M.