Adobe Acrobat prompts saving

[Romain Sarry]

Hello,

I'm using Apache PDFBox version 2.0.16 to add paging to an existing PDF
file.
My method is working great, the generated PDF is fine. However, when I open
the file with Adobe Acrobat Reader, if I try to close the file, it prompts
an alert asking me if I want to save the file even though I haven't edited
anything, and the file is not editable at first.
I can't manage to understand what's happening, and how to prevent it from
prompting saving

My code is the following :

private void paging(ByteArrayOutputStream os) throws IOException {
    PDDocument doc = PDDocument.load(new
ByteArrayInputStream(os.toByteArray()));
    PDFont font = getFont(doc);
    PDPageTree pages = doc.getDocumentCatalog().getPages();
    for (int i = 0; i < pages.getCount(); i++) {
        PDPage page = pages.get(i);
        PDPageContentStream contentStream = new
PDPageContentStream(doc, page, PDPageContentStream.AppendMode.APPEND,
true, false);
        contentStream.beginText();
        contentStream.setFont(font, FONT_SIZE);
        contentStream.setNonStrokingColor(Color.BLACK);
        contentStream.newLineAtOffset(page.getCropBox().getWidth() - 40,  15);
        contentStream.showText((i + 1) + " / " + pages.getCount());
        contentStream.endText();
        contentStream.close();
    }

    doc.save(os);
    doc.close();
}


*Romain SARRY*

*Ingénieur en Développement*
*06 29 08 34 02*
*13 rue des Teinturiers **69100 Villeurbanne*