我正在使用pdfbox并排连接两个pdf。我正在使用以下代码：

PDDocument outDoc = new PDDocument();
    int maxPages = targetDoc.getNumberOfPages();
    if(sourceDoc.getNumberOfPages()>targetDoc.getNumberOfPages()){
        maxPages = sourceDoc.getNumberOfPages();
    }
    PDPage sourceIndexPage;
    PDPage targetIndexPage;
    PDRectangle pdf1Frame;
    PDRectangle pdf2Frame;
    PDRectangle outPdfFrame;
    COSDictionary dict;
    PDPage outPdfPage;
    LayerUtility layerUtility;
    PDFormXObject sourceFormPDF;
    PDFormXObject targetFormPDF;
    AffineTransform afLeft;
    AffineTransform afRight;
    for(int indexPage =0; indexPage < maxPages; indexPage++) {
        // Create output PDF frame
        try {
            sourceIndexPage = sourceDoc.getPage(indexPage);
        }catch(IndexOutOfBoundsException error){
            sourceDoc.addPage(new PDPage());
            sourceIndexPage = targetDoc.getPage(indexPage);         }
        try {
            targetIndexPage = targetDoc.getPage(indexPage);
        }catch (IndexOutOfBoundsException error){
            targetDoc.addPage(new PDPage());
            targetIndexPage = targetDoc.getPage(indexPage);
        }
        sourceIndexPage.setRotation(0);
        targetIndexPage.setRotation(0);
        pdf1Frame = sourceIndexPage.getCropBox();
        pdf2Frame = targetIndexPage.getCropBox();
        outPdfFrame = new PDRectangle(pdf1Frame.getWidth() + pdf2Frame.getWidth(),
                Math.max(pdf1Frame.getHeight(), pdf2Frame.getHeight()));
        // Create output page with calculated frame and add it to the document
        dict = new COSDictionary();
        dict.setItem(COSName.TYPE, COSName.PAGE);
        dict.setItem(COSName.MEDIA_BOX, outPdfFrame);
        dict.setItem(COSName.CROP_BOX, outPdfFrame);
        dict.setItem(COSName.ART_BOX, outPdfFrame);
        outPdfPage = new PDPage(dict);
        outDoc.addPage(outPdfPage);
        // Source PDF pages has to be imported as form XObjects to be able to insert them at a specific point in the output page
        // pageNumber
        layerUtility = new LayerUtility(outDoc);
        sourceFormPDF = layerUtility.importPageAsForm(sourceDoc, indexPage);
        targetFormPDF = layerUtility.importPageAsForm(targetDoc, indexPage);
        // Add form objects to output page
        afLeft = new AffineTransform();
        layerUtility.appendFormAsLayer(outPdfPage, sourceFormPDF, afLeft, "left "+ indexPage);
        afRight = AffineTransform.getTranslateInstance(pdf1Frame.getWidth(), 0.0);
        layerUtility.appendFormAsLayer(outPdfPage, targetFormPDF, afRight, "right"+ indexPage);
    }
    outDoc.save("oudDoc.pdf");

我的问题是，对于某些文档，outdoc的大小太大。我期望它是暗淡的源文档+暗淡的目标文档，但实际上它是10倍，20倍以上。
查看文档结构内部，我注意到我正在重复原始PDF中分离的公共资源。有没有办法压缩/优化我的代码以减少磁盘空间？