So the question is, does Russia really have a hard time getting spies in? Or is it more of a matter of saving money on the travel effort and letting a couple local kids be the fall guys? Because the recruitment itself has some risk. Netherlands probably needs some counter spies posing as kids looking to be recruited.

I’ve been using JSignPDF for this by running:

java -jar jsignpdf-1.6.1/JSignPdf.jar

The tool you link looks quite a bit more comprehensive and user friendly. I think w/JSignPDF it just does the task of signing. You still need to generate SSL certs. I’ve not tried docuseal but looks like it tries to be foolproof.