Replace Pages but maintain PDF Forms Elements with iText7 and C#

Question

I have a PDF Form (with form fields as textbox, radiobutton, same textbox on different pages and so on.) Now I would like to exchange for example page no. 2 with page no.2 of a different pdf. But the current form fields existing on page 2 should stay as they are. The code below works fine for "simple" textfields. But I find no example in the web for radiobuttons and textfields with the same name on different pages...

Can anybody help?

using (PdfReader read = new(resultFilename))
using (PdfWriter write = new(fileTemp))
using (PdfDocument pdfDoc = new(read, write))
using (PdfReader replaceRead = new(replaceFilename))

using (PdfDocument replacePdfDoc = new(replaceRead))
{
    Document document = new(pdfDoc);
    int resultPages = pdfDoc.GetNumberOfPages();
    int replacePages = replacePdfDoc.GetNumberOfPages();
    replacePdfDoc.CopyPagesTo(1, resultPages, pdfDoc);

    PdfAcroForm form = PdfAcroForm.GetAcroForm(pdfDoc, true);
    form.SetGenerateAppearance(true);
    var fields = form.GetFormFields();

    foreach (var field in fields)
    {
        PdfFormField ff = field.Value;

        if (ff == null)
            continue;

        IList<iText.Kernel.Pdf.Annot.PdfWidgetAnnotation> pdfWidgetAnnotations = ff.GetWidgets();

        PdfPage page = pdfWidgetAnnotations[0].GetPage();
        int number = pdfDoc.GetPageNumber(page);

        if (number <= resultPages)
            number += resultPages;

        if (ff.GetParent() != null)
            continue;

        pdfDoc.GetPage(number).AddAnnotation(pdfWidgetAnnotations[0]);
    }

    for (int i = 1; i <= resultPages; i++)
    {
        pdfDoc.RemovePage(1);
    }
}