Is overriding Pimcore Pdf Model supported?

Is overriding \Pimcore\Model\Document\Tag\Pdf supported as documented in
guide? (For some reason my implementation is never called)…

If not supported, how to get pdfreactor to render pdf asset correctly so that the asset gets embedded into the resulting document? With default \Pimcore\Model\Document\Tag\Pdf::frontend() implementation (the method I would like to override) the outcome is empty thumbnail placeholder with an invalid link. So the pdf asset is not printed in the resulting pdf.

Here’s the changed part of my pimcore implementation to fix the issue:

$code = <<<HTML <div id="$divId" class="pimcore-pdfViewer"> <img src="$pdfPath" /> </div> HTML;

But my overrided pimcore pdf model is never called and I wouldn’t like to fork the pimcore…

it is not supported by the overriding models functionality (since the editable is no model), but you can add custom editables with this guide.
So, it also should be possible to overwrite existing editables by just providing your custom implementation for an core editable in the configuration (step 2 in guide).