The PDF Converter Services Online uses a Swagger file to describe the facilities exposed by the REST API. The main advantage of using Swagger is that it can be used to generate wrappers / proxies / clients for an absolutely staggering number of languages, servers and platforms.
Pre-generated clients and sample code for the most popular platforms can be found here.
If your platform is not listed then you can generate your own client using editor.swagger.io or Codegen.