    @Test
    public void testPdfAlphaImageReplacing() throws Exception {

        InputStream stream = AlterPDFParserTest.class.getResourceAsStream("/test-documents/transp_scanned.pdf");
        PDDocument doc = PDDocument.load(stream);

        PdfContentImagePreprocessor preproc = new PdfContentImagePreprocessor();
        boolean hasReplaced = preproc.removeImagesAlphaChannel(doc);
        assertTrue(hasReplaced);
    }