Adding a signature form field to a page it's visible in the last page also

Question

I'm trying to put signature form fields in a given position at specific pages using iText for .NET (v7.0.4). The code I'm working on is the following:

public static void test()
    {
        using (PdfDocument pdfDoc = new PdfDocument(new PdfWriter(@"c:\temp\pippo.pdf")))
        {
            //Add some blank pages
            pdfDoc.AddNewPage();
            pdfDoc.AddNewPage();
            pdfDoc.AddNewPage();

            //Instantiate a Signature Form Field using factory
            PdfSignatureFormField sgnField = 
                PdfFormField.CreateSignature(pdfDoc, new Rectangle(100, 100, 200, 100));

            //setting name and page
            sgnField.SetFieldName("pluto");
            sgnField.SetPage(1);

            //Adding to AcroForm
            PdfAcroForm.GetAcroForm(pdfDoc, true).AddField(sgnField);
        }
    }

The output document (pippo.pdf) has the signature field in first page and that's the expected behavior. The issue is that I can see the signature field even in the last page (the third page, in this case).

Moreover, if I remove the last page, by calling pdfDoc.RemovePage(3);, the signature field disappear even from the first page.

The question is: how to make signature form fields not replicated in the last page? Any suggestion is really well accepted!

Answer 1

The method AddField(PdfFormField field) is documented as

 * This method adds the field to the last page in the document.
 * If there's no pages, creates a new one.

Thus, you first assign your field to the first page using

sgnField.SetPage(1)

and then also to the last one using

PdfAcroForm.GetAcroForm(pdfDoc, true).AddField(sgnField);

You should use AddField(PdfFormField field, PdfPage page) instead:

PdfAcroForm.GetAcroForm(pdfDoc, true).AddField(sgnField, pdfDoc.GetFirstPage());

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@iText DEV: When going for PDF2, this should be prevented.