Exception in thread "main" java.lang.reflect.InvocationTargetException

I am using iText PDF 5.5.11 to convert PDF to XML.I already checked similar answers on stackoverflow. I am getting below error when I run jar file using command line on ubuntu. java version "1.8.0_101"

 Exception in thread "main" java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.eclipse.jdt.internal.jarinjarloader.JarRsrcLoader.main(JarRsrcLoader.java:58)
Caused by: java.lang.NoClassDefFoundError: org/bouncycastle/asn1/ASN1Encodable
    at com.itextpdf.text.pdf.PdfEncryption.<init>(PdfEncryption.java:147)
    at com.itextpdf.text.pdf.PdfReader.readDecryptedDocObj(PdfReader.java:1063)
    at com.itextpdf.text.pdf.PdfReader.readDocObj(PdfReader.java:1469)
    at com.itextpdf.text.pdf.PdfReader.readPdf(PdfReader.java:751)
    at com.itextpdf.text.pdf.PdfReader.<init>(PdfReader.java:198)
    at com.itextpdf.text.pdf.PdfReader.<init>(PdfReader.java:236)
    at com.itextpdf.text.pdf.PdfReader.<init>(PdfReader.java:224)
    at com.itextpdf.text.pdf.PdfReader.<init>(PdfReader.java:214)
    at test.pdfreader.readXml(pdfreader.java:34)
    at test.pdfreader.main(pdfreader.java:30)

I am not much familiar with java. I call this jar file from PHP using PHP exec function. Below is the code I use to convert PDF to XML.

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.AcroFields;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.XfaForm;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class pdfreader {
    public static void main(String[] args) throws IOException, DocumentException, TransformerException {
        String SRC = "";
        String DEST = "";

        for (String s : args) {
            SRC = args[0];
            DEST = args[1];
        }
        File file = new File(DEST);
        file.getParentFile().mkdirs();
        new pdfreader().readXml(SRC, DEST);
    }

    public void readXml(String src, String dest) throws IOException, DocumentException, TransformerException {
        PdfReader reader = new PdfReader(src);

        AcroFields form = reader.getAcroFields();
        XfaForm xfa = form.getXfa();
        Node node = xfa.getDatasetsNode();
        NodeList list = node.getChildNodes();
        for (int i = 0; i < list.getLength(); ++i) {
            if ("data".equals(list.item(i).getLocalName())) {
                node = list.item(i);

                break;
            }
        }
        list = node.getChildNodes();

        Transformer tf = TransformerFactory.newInstance().newTransformer();
        tf.setOutputProperty("encoding", "UTF-8");
        tf.setOutputProperty("indent", "yes");
        FileOutputStream os = new FileOutputStream(dest);

        tf.transform(new DOMSource(node), new StreamResult(os));
        reader.close();
    }
}