Ok. You want to use the pdf-utils exension.
Here you can find the .net example
https://github.com/jsreport/jsreport-pdf-utils/issues/12#issuecomment-428584744
However I would recommend to read through the docs and try provided examples for the start to get how it works as this is quite more advanced.
I think it is usually better to start with jsreport studio and afterwards try to translate it into .net if you need the embedded .net integration.