create a one page PDF from two PDFs using PDFBOX

Question

I have a small (quarter inch) one page PDF I created with PDFBOX with text (A). I want to put that small one page PDF (A) on the top of an existing PDF page (B), preserving the existing content of the PDF page (B). In the end, I will have a one page PDF, representing the small PDF on top(A), and the existing PDF intact making up the rest (B). How can I accomplish this with PDFBOX?

Answer 1

To join two pages one atop the other onto one target page, you can make use of the PDFBox LayerUtility for importing pages as form XObjects in a fashion similar to PDFBox SuperimposePage example, eg with this helper method:

void join(PDDocument target, PDDocument topSource, PDDocument bottomSource) throws IOException {
    LayerUtility layerUtility = new LayerUtility(target);
    PDFormXObject topForm = layerUtility.importPageAsForm(topSource, 0);
    PDFormXObject bottomForm = layerUtility.importPageAsForm(bottomSource, 0);

    float height = topForm.getBBox().getHeight() + bottomForm.getBBox().getHeight();
    float width, topMargin, bottomMargin;
    if (topForm.getBBox().getWidth() > bottomForm.getBBox().getWidth()) {
        width = topForm.getBBox().getWidth();
        topMargin = 0;
        bottomMargin = (topForm.getBBox().getWidth() - bottomForm.getBBox().getWidth()) / 2;
    } else {
        width = bottomForm.getBBox().getWidth();
        topMargin = (bottomForm.getBBox().getWidth() - topForm.getBBox().getWidth()) / 2;
        bottomMargin = 0;
    }

    PDPage targetPage = new PDPage(new PDRectangle(width, height));
    target.addPage(targetPage);


    PDPageContentStream contentStream = new PDPageContentStream(target, targetPage);
    if (bottomMargin != 0)
        contentStream.transform(Matrix.getTranslateInstance(bottomMargin, 0));
    contentStream.drawForm(bottomForm);
    contentStream.transform(Matrix.getTranslateInstance(topMargin - bottomMargin, bottomForm.getBBox().getHeight()));
    contentStream.drawForm(topForm);
    contentStream.close();
}

( JoinPages method join )

You use it like this:

try (   PDDocument document = new PDDocument();
        PDDocument top = ...;
        PDDocument bottom = ...) {
    join(document, top, bottom);
    document.save("joinedPage.pdf");
}

( JoinPages test testJoinSmallAndBig )

The result looks like this:

Answer 2

Just as an additional point to @mkl's answer. If anybody is looking to scale the PDFs before placing them on the page use,

    contentStream.transform(Matrix.getScaleInstance(<scaling factor in x axis>, <scaling factor in y axis>));  //where 1 is the scaling factor if you want the page as the original size

This way you can rescale your PDFs.