code: public ConverterServerBuilder enable(Class<? extends IExternalConverter> externalConverter) {
          converterConfiguration.put(externalConverter, Boolean.TRUE);
          return this;
      }
docs: Enables the given {@link com.documents4j.conversion.IExternalConverter}. Any converter that is shipped with
  this library is discovered automatically from the class path and does not need to be enabled explicitly.
  
  @param externalConverter The converter to be enabled.
  @return This builder.