PDFBox Signature Field not well recognized - pdf

Question

I'm going in trouble using PDFBox 2.0.0-RC3 and producing a digital signature field into a PDF.
This is the piece of code i use:
public static void main(String[] args) throws IOException, URISyntaxException
{
PDDocument document;
document = new PDDocument();
PDPage page = new PDPage(PDRectangle.A4);
document.addPage(page);
PDAcroForm acroForm = new PDAcroForm(document);
document.getDocumentCatalog().setAcroForm(acroForm);
PDSignatureField signatureBox = new PDSignatureField(acroForm);
signatureBox.setPartialName("ENSGN-MY_SIGNATURE_FIELD-001");
acroForm.getFields().add(signatureBox);
PDAnnotationWidget widget = signatureBox.getWidgets().get(0);
PDRectangle rect = new PDRectangle();
rect.setLowerLeftX(50);
rect.setLowerLeftY(750);
rect.setUpperRightX(250);
rect.setUpperRightY(800);
widget.setRectangle(rect);
page.getAnnotations().add(widget);
try {
document.save("/tmp/mySignatureFieldGEN_PDFBOX.pdf");
document.close();
} catch (Exception io) {
System.out.println(io);
}
}
The code generates a pdf document, i open it with Acrobat Reader and this is the result:
PDF BOX Generated
As you can see, the signature panel on the left is void but the signature field on the left is present and works.
I generate the same PDF with PDFTron. This is the result:
PDF Tron Generated
In this case the signature panel on the left show correctly the presence of the signature field.
I would like to obtain this second case (correct) but i don't understand why PDF Box can do this.
Many thanks

Answer 1

add this:
widget.setPage(page);
This sets the /P entry.
Now the panel on the left appears. How did I get the idea? I got a document with such an empty signature field (from here), and compared it with yours with PDFDebugger.