Hello,
You can add footnotes to specific contents in sections (MS Word doesn't work with pages but with sections) using DOCXPath (https://www.phpdocx.com/documentation/introduction/docxpath).
If you need to add a custom footer, you'd need to import the footer from an existing DOCX (from a template or generated from scratch using phpdocx) and then use DOCXPath to replace the previous footer.
Regards.