extension api for pdf backend

is it possible to use extentions (for example, PostProcessor) in my own program, that uses asciidoctorj-pdf? i tried to do this (EndToEndPostProcessor is my own class):

public class DoctorRun {

    public static void main(String[] args) {
        Asciidoctor asciidoctor = create();
        asciidoctor.javaExtensionRegistry().postprocessor(new EndToEndPostProcessor(options().backend("pdf").asMap()));
        asciidoctor.convertFile(new File("D:\\\\rc-req-mb-client\\src\\main.adoc"), options().backend("pdf").get());
    }

}

and received following output (in IntelliJ IDEA):

"C:\Program Files\Java\jdk1.8.0_91\bin\java" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:61162,suspend=y,server=n -Djruby.aot.loadClasses=true -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_91\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_91\jre\lib\rt.jar;D:\asciidoctorprocessor\target\classes;C:\Users\itimofeev\.m2\repository\org\asciidoctor\asciidoctorj\1.5.6\asciidoctorj-1.5.6.jar;C:\Users\itimofeev\.m2\repository\org\jruby\jruby-complete\1.7.26\jruby-complete-1.7.26.jar;C:\Users\itimofeev\.m2\repository\com\beust\jcommander\1.35\jcommander-1.35.jar;C:\Users\itimofeev\.m2\repository\org\asciidoctor\asciidoctorj-pdf\1.5.0-alpha.11\asciidoctorj-pdf-1.5.0-alpha.11.jar;C:\Users\itimofeev\.m2\repository\org\jsoup\jsoup\1.8.3\jsoup-1.8.3.jar;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 15.0.3\lib\idea_rt.jar" cz.bsc.asciidoctorprocessor.DoctorRun
Connected to the target VM, address: '127.0.0.1:61162', transport: 'socket'
Disconnected from the target VM, address: '127.0.0.1:61162', transport: 'socket'
авг 24, 2017 8:16:33 PM org.asciidoctor.internal.JRubyAsciidoctor renderFile
SEVERE: (NameError) no method 'process' for arguments (org.jruby.RubyObject,org.jruby.RubyObject) on Java::CzBscAsciidoctorprocessor::EndToEndPostProcessor
  available overloads:
    (org.asciidoctor.ast.Document,java.lang.String)
    (org.asciidoctor.ast.DocumentRuby,java.lang.String)
Exception in thread "main" org.asciidoctor.internal.AsciidoctorCoreException: org.jruby.exceptions.RaiseException: (NameError) no method 'process' for arguments (org.jruby.RubyObject,org.jruby.RubyObject) on Java::CzBscAsciidoctorprocessor::EndToEndPostProcessor
  available overloads:
    (org.asciidoctor.ast.Document,java.lang.String)
    (org.asciidoctor.ast.DocumentRuby,java.lang.String)
    at org.asciidoctor.internal.JRubyAsciidoctor.renderFile(JRubyAsciidoctor.java:347)
    at org.asciidoctor.internal.JRubyAsciidoctor.renderFile(JRubyAsciidoctor.java:436)
    at org.asciidoctor.internal.JRubyAsciidoctor.convertFile(JRubyAsciidoctor.java:556)
    at cz.bsc.asciidoctorprocessor.DoctorRun.main(DoctorRun.java:18)
Caused by: org.jruby.exceptions.RaiseException: (NameError) no method 'process' for arguments (org.jruby.RubyObject,org.jruby.RubyObject) on Java::CzBscAsciidoctorprocessor::EndToEndPostProcessor
  available overloads:
    (org.asciidoctor.ast.Document,java.lang.String)
    (org.asciidoctor.ast.DocumentRuby,java.lang.String)
    at org.jruby.RubyMethod.call(org/jruby/RubyMethod.java:124)
    at RUBY.convert(C:/Users/itimofeev/.m2/repository/org/asciidoctor/asciidoctorj/1.5.6/asciidoctorj-1.5.6.jar!/gems/asciidoctor-1.5.6.1/lib/asciidoctor/document.rb:1066)
    at org.jruby.RubyArray.each(org/jruby/RubyArray.java:1613)
    at RUBY.convert(C:/Users/itimofeev/.m2/repository/org/asciidoctor/asciidoctorj/1.5.6/asciidoctorj-1.5.6.jar!/gems/asciidoctor-1.5.6.1/lib/asciidoctor/document.rb:1065)
    at RUBY.convert(C:/Users/itimofeev/.m2/repository/org/asciidoctor/asciidoctorj/1.5.6/asciidoctorj-1.5.6.jar!/gems/asciidoctor-1.5.6.1/lib/asciidoctor.rb:1502)
    at RUBY.convert_file(C:/Users/itimofeev/.m2/repository/org/asciidoctor/asciidoctorj/1.5.6/asciidoctorj-1.5.6.jar!/gems/asciidoctor-1.5.6.1/lib/asciidoctor.rb:1575)
    at org.jruby.RubyIO.open(org/jruby/RubyIO.java:1201)
    at RUBY.convert_file(C:/Users/itimofeev/.m2/repository/org/asciidoctor/asciidoctorj/1.5.6/asciidoctorj-1.5.6.jar!/gems/asciidoctor-1.5.6.1/lib/asciidoctor.rb:1575)
    at RUBY.convertFile(<script>:75)
    at org.jruby.gen.InterfaceImpl1333197270.convertFile(org/jruby/gen/InterfaceImpl1333197270.gen:13)

Process finished with exit code 1

How to fix it? What is wrong?

asciidoctor / asciidoctorj-pdf

extension api for pdf backend #7