This sample draws two stars on a PDF Page using two different techniques.

DrawingPolygons.java

/*
 * Copyright Datalogics, Inc. 2015
 */

package pdfjt.cookbook.document;

import com.adobe.fontengine.font.Font;
import com.adobe.internal.io.ByteReader;
import com.adobe.internal.io.InputStreamByteReader;
import com.adobe.pdfjt.core.types.ASName;
import com.adobe.pdfjt.pdf.content.Content;
import com.adobe.pdfjt.pdf.content.InstructionFactory;
import com.adobe.pdfjt.pdf.contentmodify.ContentWriter;
import com.adobe.pdfjt.pdf.contentmodify.ModifiableContent;
import com.adobe.pdfjt.pdf.document.PDFContents;
import com.adobe.pdfjt.pdf.document.PDFDocument;
import com.adobe.pdfjt.pdf.document.PDFOpenOptions;
import com.adobe.pdfjt.pdf.document.PDFResources;
import com.adobe.pdfjt.pdf.graphics.font.PDFFont;
import com.adobe.pdfjt.pdf.interactive.annotation.PDFAnnotationEnum;
import com.adobe.pdfjt.pdf.interactive.annotation.PDFAnnotationPolygon;
import com.adobe.pdfjt.pdf.interactive.annotation.PDFBorder;
import com.adobe.pdfjt.pdf.page.PDFPage;
import com.adobe.pdfjt.services.ap.AppearanceService;
import com.adobe.pdfjt.services.ap.spi.APContext;
import com.adobe.pdfjt.services.ap.spi.APResources;
import com.datalogics.pdf.document.DocumentHelper;

import java.awt.Point;
import java.awt.Shape;
import java.awt.geom.GeneralPath;
import java.awt.geom.PathIterator;
import java.awt.geom.Point2D;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.EnumSet;
import java.util.HashMap;

/**
 *  This sample draws two stars on a PDF Page using two different techniques.
 */
public class DrawingPolygons {

    private static final String inputPDFURL = "http://dev.datalogics.com/cookbook/annotations/Polygons.pdf";
    private static final String outputDir = "cookbook/Annotations/output/";
    private static final double red[] = { 1.0, 0, 0 }; // RGB Red

    static public void main(String[] args) throws Exception {

        // First read in the PDF file
        URLConnection connection = new URL(inputPDFURL).openConnection();
        connection.setRequestProperty("User-Agent",
                "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.95 Safari/537.11");
        connection.connect();
        InputStream fis = connection.getInputStream();
        ByteReader byteReader = new InputStreamByteReader(fis);
        PDFDocument pdfDocument = PDFDocument.newInstance(byteReader, PDFOpenOptions.newInstance());
        /*
         * Then get the first (and only) page in the file. We'll need this
         * object in order to add content and annotations to it.
         */
        PDFPage pdfPageOne = pdfDocument.requirePages().getPage(0);

        int numArms = 5;
        Double contentCenterX = pdfPageOne.getMediaBox().width() / 4;
        Double contentCenterY = pdfPageOne.getMediaBox().height() / 4 * 3;
        Point contentCenter = new Point(contentCenterX.intValue(), contentCenterY.intValue());
        Shape starContent = createStar(numArms, contentCenter, 72, 36);

        /*
         * Now create a ContentWriter so we can write new page content to the PDF
         */
        PDFContents pdfContents = PDFContents.newInstance(pdfPageOne.getPDFDocument());
        PDFResources pdfResources = PDFResources.newInstance(pdfPageOne.getPDFDocument());
        ContentWriter contentWriter = ContentWriter.newInstance(ModifiableContent.newInstance(pdfContents, pdfResources));
        // Set the thickness of any lines drawn after this instruction
        contentWriter.write(InstructionFactory.newLineWidth(.5));

        // Use the coordinates of the shape to create the PDF drawing Instructions
        double[] contentCoordinates = new double[6];
        for (PathIterator pathIterator = starContent.getPathIterator(null); !pathIterator.isDone(); pathIterator.next()) {
            int type = pathIterator.currentSegment(contentCoordinates);
            if (type == PathIterator.SEG_MOVETO) {
                contentWriter.write(InstructionFactory.newMoveTo(contentCoordinates[0], contentCoordinates[1]));
            }
            if (type == PathIterator.SEG_LINETO) {
                contentWriter.write(InstructionFactory.newLineTo(contentCoordinates[0], contentCoordinates[1]));
            }
            if (type == PathIterator.SEG_CLOSE) {
                contentWriter.write(InstructionFactory.newCloseAndStrokePath());
            }
        }
        Content content = contentWriter.close();
        // Add the new content to the existing page content
        pdfPageOne.getContents().addContents(content.getContentStream());

        // Create a new shape next to the first one
        Double annotCenterX = pdfPageOne.getMediaBox().width() / 4 * 3;
        Double annotCenterY = pdfPageOne.getMediaBox().height() / 4 * 3;
        Point annotCenter = new Point(annotCenterX.intValue(), annotCenterY.intValue());
        Shape starAnnot = createStar(numArms, annotCenter, 72, 36);
        
        /*
         * Create an array to hold the vertices. The length of the array equals
         * the number of arms times two, one for each inner vertex and outer
         * vertex of the star, plus one to return to the origin, then double
         * that number since we need the x and y coordinates to be in the same array.
         */
        double[] vertices = new double[((numArms * 2) + 1) * 2];
        /*
         * Now use the coordinates of the Shape to create the array that we'll use in the annotation Vertices dictionary.
         */
        double[] coordinates = new double[6];
        int i = 0;
        for (PathIterator pathIterator = starAnnot.getPathIterator(null); !pathIterator.isDone(); pathIterator.next()) {
            pathIterator.currentSegment(coordinates);
            vertices[i] = coordinates[0];
            vertices[i + 1] = coordinates[1];
            i += 2;
        }
        
        // Now add the annotation to the page.

        PDFAnnotationPolygon pdfAnnotationPolygon = PDFAnnotationPolygon.newInstance(pdfDocument);
        pdfAnnotationPolygon.setDictionaryArrayValue(ASName.k_Vertices, vertices);
        pdfAnnotationPolygon.setColor(red);
        PDFBorder pdfBorder = PDFBorder.newInstance(pdfDocument);
        pdfBorder.setWidth(.5);
        pdfAnnotationPolygon.setBorder(pdfBorder);
        pdfPageOne.addAnnotation(pdfAnnotationPolygon);

        // Now create the appearances of the Polygon annotations
        APResources apResources = new APResources(pdfDocument.getCosDocument().getOptions().getFontSet(),
                pdfDocument.getCosDocument().getOptions().getDocLocale(), new HashMap<Font, PDFFont>());
        APContext apContext = new APContext(apResources, true, null);
        apContext.setAnnotationsToBeProcessed(EnumSet.of(PDFAnnotationEnum.Polygon));
        AppearanceService.generateAppearances(pdfDocument, apContext, null);

        // Save and close
        DocumentHelper.saveFullAndClose(pdfDocument, outputDir + "Polygons.pdf");

        // Save the file.
        System.out.println("Done!");
    }

    /*
     * From:
     * http://stackoverflow.com/questions/2710065/drawing-star-shapes-with-
     * variable-parameters By Peter Walser -
     * http://stackoverflow.com/users/63293/peter-walser
     */
    public static Shape createStar(int arms, Point center, double rOuter, double rInner) {
        double angle = Math.PI / arms;
        GeneralPath path = new GeneralPath();
        for (int i = 0; i < 2 * arms; i++) {
            double r = (i & 1) == 0 ? rOuter : rInner;
            Point2D.Double p = new Point2D.Double(center.x + Math.cos(i * angle) * r, center.y + Math.sin(i * angle) * r);
            if (i == 0)
                path.moveTo(p.getX(), p.getY());
            else
                path.lineTo(p.getX(), p.getY());
        }
        path.closePath();
        return path;
    }
}