Using the iText signature PDF file on Android

build.gradle

dependencies {
    compile 'com.itextpdf:itextg:5.5.10'
    compile "com.madgag:scprov-jdk15on:1.47.0.2"
    compile "com.madgag:scpkix-jdk15on:1.47.0.2"
}

Util.java

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Image;
import com.itextpdf.text.Paragraph;
import com.itextpdf.text.Rectangle;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfSignatureAppearance;
import com.itextpdf.text.pdf.PdfStamper;
import com.itextpdf.text.pdf.PdfWriter;
import com.itextpdf.text.pdf.security.BouncyCastleDigest;
import com.itextpdf.text.pdf.security.DigestAlgorithms;
import com.itextpdf.text.pdf.security.ExternalDigest;
import com.itextpdf.text.pdf.security.ExternalSignature;
import com.itextpdf.text.pdf.security.MakeSignature;
import com.itextpdf.text.pdf.security.PrivateKeySignature;
import com.itextpdf.text.pdf.security.TSAClient;
import com.itextpdf.text.pdf.security.TSAClientBouncyCastle;

import org.spongycastle.jce.provider.BouncyCastleProvider;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.PrivateKey;
import java.security.Security;
import java.security.cert.Certificate;

/**
 * @author FingerArt http://fingerart.me
 * @date 2017年08月10日 18:46
 */
public class Ut {
    
    static {
        Security.insertProviderAt(new BouncyCastleProvider(), 1);
    }

    /**
     * Creates a PDF document.
     *
     * @param filename the path to the new PDF document
     * @throws DocumentException
     * @throws IOException
     */
    public static void createPdf(String filename, String content) throws IOException, DocumentException {
        Document document = null;
        PdfWriter writer = null;
        try {
            document = new Document();
            writer = PdfWriter.getInstance(document, new FileOutputStream(filename));
            document.open();
            document.add(new Paragraph(content));
        } finally {
            if (document != null) {
                document.close();
            }
            if (writer != null) {
                writer.close();
            }
        }
    }

    /**
     * Manipulates a PDF file src with the file dest as result
     *
     * @param src  the original PDF
     * @param dest the resulting PDF
     * @param tsaUrl
     * @throws GeneralSecurityException
     * @throws IOException
     * @throws DocumentException
     * @throws FileNotFoundException
     * @throws KeyStoreException
     * @throws Exception
     */
    static void signPdf(@NonNull String src, @NonNull String dest, InputStream pdfCerStream, @NonNull String keystorePassword, @NonNull String keyPassword, String reason, String location, @Nullable String signatureImage, String tsaUrl) throws GeneralSecurityException, IOException, DocumentException {
        // private key and certificate
        KeyStore ks = KeyStore.getInstance("pkcs12", "BC");
        ks.load(pdfCerStream, keystorePassword.toCharArray());
        String alias = ks.aliases().nextElement();
        PrivateKey pk = (PrivateKey) ks.getKey(alias, keyPassword.toCharArray());
        Certificate[] chain = ks.getCertificateChain(alias);
        // reader and stamper
        PdfReader reader = new PdfReader(src);
        PdfStamper stamper = PdfStamper.createSignature(reader, new FileOutputStream(dest), '\0');
        // appearance
        PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
        appearance.setReason(reason);
        appearance.setLocation(location);
        appearance.setVisibleSignature(new Rectangle(72, 732, 144, 780), reader.getNumberOfPages(), "sign");
        appearance.setCertificationLevel(PdfSignatureAppearance.CERTIFIED_NO_CHANGES_ALLOWED);
        if (signatureImage != null && !signatureImage.isEmpty()) {
            appearance.setSignatureGraphic(Image.getInstance(signatureImage));
            appearance.setRenderingMode(PdfSignatureAppearance.RenderingMode.GRAPHIC_AND_DESCRIPTION);
        }
        // signature
        TSAClient tsaClient = new TSAClientBouncyCastle(tsaUrl, null, null, 6500, DigestAlgorithms.SHA256);
        ExternalSignature es = new PrivateKeySignature(pk, DigestAlgorithms.SHA256, "BC");
        ExternalDigest digest = new BouncyCastleDigest();
        MakeSignature.signDetached(appearance, digest, es, chain, null, null, tsaClient, 0, MakeSignature.CryptoStandard.CMS);
    }
}