How to reduce the size of merged PDF/A-1b files with pdfbox or other java library

Question

Input: A list of (e.g. 14) PDF/A-1b files with embedded fonts.
Processing: Doing a simple merge with Apache PDFBOX.
Result<

Answer 1

An other way I found is using ITEXT 7 that way (pdfWriter.setSmartMode):

    try (PdfWriter pdfWriter = new PdfWriter(out)) {
        pdfWriter.setSmartMode(true); // Here happens the optimation, e.g. reducing redundantly embedded fonts
        pdfWriter.setCompressionLevel(Deflater.BEST_COMPRESSION);
        try (PdfDocument pdfDoc = new PdfADocument(pdfWriter, PdfAConformanceLevel.PDF_A_1B,
                new PdfOutputIntent("Custom", "", "http://www.color.org", "sRGB IEC61966-2.1", colorProfile))) {
            PdfMerger merger = new PdfMerger(pdfDoc);
            merger.setCloseSourceDocuments(true);
            try {
                for (InputStream pdf : pdfs) {
                    try (PdfDocument doc = new PdfDocument(new PdfReader(pdf))) {
                        merger.merge(doc, createPageList(doc.getNumberOfPages()));
                    }
                }
                merger.close();
            }
            catch (com.itextpdf.kernel.crypto.BadPasswordException e) {
                throw new BieneException("Konkatenierung eines passwortgeschützten PDF-Dokumentes nicht möglich: " + e.getMessage(),
                        e);
            }
            catch (com.itextpdf.io.IOException | PdfException e) {
                throw new BieneException(e.getMessage(), e);
            }
        }
    }