Hi, Thomas (one of the creators) here. This is actually the reason, why we are still supporting JRE8 with open-pdf-sign instead of having a JRE11 (or later) baseline. We are offering a npm module as well (https://github.com/open-pdf-sign/open-pdf-sign-node). While that does not get rid of the JRE requirement, it makes integration in "modern" backends easier.