Hi,
I can develop that digital signature functionality for PDF and connect it with your server.
Please contact me for more details and samples of my work.
Over 10 years of experience in PHP, WordPress, Magento, HTML5, PostCSS, CSS Modules, LESS, NodeJS, AngularJS, ElasticSearch, ReactJS, Gulp, AWS, MySQL, MongoDB, Socket.io.
Best regards,
Dmitry