我写了这个奇怪的代码，它适用于我（ Apache PDFBox v.2.0.8 ）：

I wrote this strange code and it works for me (Apache PDFBox v.2.0.8):

private void saveCompressedPDF(PDDocument srcDoc, OutputStream os) throws IOException {
    PDDocument outDoc = new PDDocument();
    outDoc.setDocumentInformation(srcDoc.getDocumentInformation());
    for (PDPage srcPage : srcDoc.getPages()) {
        new PDPageContentStream(outDoc, srcPage,
                PDPageContentStream.AppendMode.APPEND, true).close();
        outDoc.addPage(srcPage);
    }
    outDoc.save(os);
    outDoc.close();
}