Use PDFBox to get a digital signature image from a PDF?

Question

Pdfbox extract the visualization of a digital signature image. The pdfbox version is 2.0.20

What do you mean by *the digital signature image*? Do you have a signature field with a visible appearance and you want to store that appearance somehow? Or render it as a bitmap image? Or does that appearance contain a bitmap image and you want to extract that? Or does the signer certificate contain an image attribute which you want to extract? — mkl, Sep 03 '21 at 05:19
thanks for your answer, I mean like a seal,this seal is the visualization of a digital signature, i.e. a widget annotation of the corresponding signature field.I want to extract the visible signature as an image,such as `png,jpg`. — Mark, Sep 03 '21 at 06:19
Do you want to *extract an existing bitmap in the widget appearance*? Or do you want to *render the whole widget appearance as a new bitmap image*? — mkl, Sep 03 '21 at 08:37
@TilmanHausherr If I see it correctly, ExtractImages does not extract from annotation appearances. Not yet. ;) — mkl, Sep 03 '21 at 19:00
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. — Community, Sep 07 '21 at 09:07

score 0 · Accepted Answer · answered Sep 03 '21 at 18:59

There is a bitmap extraction tool (inspired by the PDFBox ExtractImages example) in this answer which we can easily change to inspect the page annotations instead of the static page content:

void extractPageAnnotationImages(PDDocument document, String fileNameFormat) throws IOException
{
    int page = 1;
    for (final PDPage pdPage : document.getPages())
    {
        final int currentPage = page;
        Map<String, PDAppearanceStream> allStreams = new HashMap<>();
        int annot = 1;
        for (PDAnnotation pdAnnotation  : pdPage.getAnnotations()) {
            PDAppearanceDictionary appearancesDictionary = pdAnnotation.getAppearance();
            Map<String, PDAppearanceEntry> dictsOrStreams = Map.of("Down", appearancesDictionary.getDownAppearance(), "Normal", appearancesDictionary.getNormalAppearance(), "Rollover", appearancesDictionary.getRolloverAppearance());
            for (Map.Entry<String, PDAppearanceEntry> entry : dictsOrStreams.entrySet()) {
                if (entry.getValue().isStream()) {
                    allStreams.put(String.format("%d-%s", annot, entry.getKey()), entry.getValue().getAppearanceStream());
                } else {
                    for (Map.Entry<COSName, PDAppearanceStream> subEntry : entry.getValue().getSubDictionary().entrySet()) {
                        allStreams.put(String.format("%d-%s.%s", annot, entry.getKey(), subEntry.getKey().getName()), subEntry.getValue());
                    }
                }
            }
            annot++;
        }

        PDFGraphicsStreamEngine pdfGraphicsStreamEngine = new PDFGraphicsStreamEngine(pdPage)
        {
            String current = null;
            
            @Override
            public void processPage(PDPage page) throws IOException {
                for (Map.Entry<String,PDAppearanceStream> entry : allStreams.entrySet()) {
                    current = entry.getKey();
                    processChildStream(entry.getValue(), pdPage);
                }
            }

            @Override
            public void drawImage(PDImage pdImage) throws IOException
            {
                if (pdImage instanceof PDImageXObject)
                {
                    Matrix ctm = getGraphicsState().getCurrentTransformationMatrix();
                    String flips = "";
                    if (ctm.getScaleX() < 0)
                        flips += "h";
                    if (ctm.getScaleY() < 0)
                        flips += "v";
                    if (flips.length() > 0)
                        flips = "-" + flips;
                    PDImageXObject image = (PDImageXObject)pdImage;
                    File file = new File(String.format(fileNameFormat, currentPage, current, flips, image.getSuffix()));
                    ImageIOUtil.writeImage(image.getImage(), image.getSuffix(), new FileOutputStream(file));
                }
            }

            @Override
            public void appendRectangle(Point2D p0, Point2D p1, Point2D p2, Point2D p3) throws IOException { }

            @Override
            public void clip(int windingRule) throws IOException { }

            @Override
            public void moveTo(float x, float y) throws IOException {  }

            @Override
            public void lineTo(float x, float y) throws IOException { }

            @Override
            public void curveTo(float x1, float y1, float x2, float y2, float x3, float y3) throws IOException {  }

            @Override
            public Point2D getCurrentPoint() throws IOException { return new Point2D.Float(); }

            @Override
            public void closePath() throws IOException { }

            @Override
            public void endPath() throws IOException { }

            @Override
            public void strokePath() throws IOException { }

            @Override
            public void fillPath(int windingRule) throws IOException { }

            @Override
            public void fillAndStrokePath(int windingRule) throws IOException { }

            @Override
            public void shadingFill(COSName shadingName) throws IOException { }
        };
        pdfGraphicsStreamEngine.processPage(pdPage);
        page++;
    }
}

(ExtractImages helper method)

You can apply it like this:

PDDocument document = ...;
extractPageAnnotationImages(document, "image-%s-%s%s.%s");

This creates the file names as image-[page: number]-[annotation: number-Down/Normal/Rollover[.variant]][reflection status].[extension]

Use PDFBox to get a digital signature image from a PDF?

1 Answers1