Hi AFAIK, this is not possible to do this.

It is possible to do SVG export, I do it with mxGraph and this should work as well in maxGraph. Then, if you send the SVG to your backend you could generate the PDF backend side. Or doing the SVG to PDF conversion in the browser, but this is probably not a performant way to achieve your goal 😄 .
SVG export involves the use of ImageExport.
There is an example here https://github.com/maxGraph/maxGraph/blob/v0.14.0/packages/html/stashed/grapheditor/www/js/Graph.js#L8188 but drawio probably provides a more up to date version of the code:

• https://github.com/jgraph/drawio/blob/v24.7.17/src/main/webapp/plugins/svgdata.js#L9
• https://github.com/jgraph/drawio/blob/v24.7.17/src/main/webapp/js/grapheditor/Graph.js#L11688

Here is the code I used (adapted from the drawio code): https://github.com/process-analytics/bpmn-visualization-js/blob/3be35d4289054f04bc7343c37613bb5a45f70a41/dev/ts/component/SvgExporter.ts#L33

In draw.io (and perhaps in the former mxGraph grapheditor examples) it is also possible to generate PDF. But this is done server side AFAIK.

[UPDATE] See also a past answer I wrote about this topic: #234 (comment)