The server never sees the complete page, as it is combined in the browser out of two or more assets; thus rendering on the server would require that the server starts a browser, and executes all the javascript to trigger the ajax call and embedd the returned value somehow into the DOM, so it can be finally rendered into the PDF.
I guess that this is somehow possible (you have to have an embedded browser like phantomjs or such), although I am not sure if the PDF generator can handle that case directly.