@Override
    public RenderResults render(InputStream is, Metadata metadata, ParseContext parseContext,
                                RenderRequest... requests) throws IOException, TikaException {


        PDDocument pdDocument;
        TikaInputStream tis = TikaInputStream.get(is);
        boolean mustClose = false;
        if (tis.getOpenContainer() != null) {
            pdDocument = (PDDocument) tis.getOpenContainer();
        } else {
            pdDocument = Loader.loadPDF(new RandomAccessReadBuffer(is));
            mustClose = true;
        }
        PageBasedRenderResults results = new PageBasedRenderResults(new TemporaryResources());
        try {
            for (RenderRequest renderRequest : requests) {
                processRequest(renderRequest, pdDocument, metadata, parseContext, results);
            }
        } finally {
            if (mustClose) {
                pdDocument.close();
            }
        }
        return results;
    }
This is the amount of time it takes for PDFBox/java to write the image after
it has been rendered into a BufferedImage.  Some formats take much longer
to encode than others.
tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-pdf-module/src/main/java/org/apache/tika/renderer/pdf/pdfbox/PDFBoxRenderer.java