Signed Signature Field gets deleted after update_page_form_field_values()

[liam-meak]

I am developing a script to automatically fill out the 'Nr' field in a timesheet form.
The forms are digitally signed before they get a number.

When updating the 'Nr' field using writer.update_page_form_field_values() the signed signature field gets deleted.
Another signature field, which has not been signed at this point, has the expected behaviour.

This happened only when using:

writer.append(reader,[0])

Before I had the issue that all radio buttons were deleted but the signature was not.
This happend when using:

page = self._reader.pages[0]
writer.add_page(page)

Environment

Which environment were you using when you encountered the problem?

$ python -m platform
Windows-10-10.0.19045-SP0

$ python -c "import Pydf2;print(pypdf.__version__)"
3.0.1

Code + PDF

This is a minimal, complete example that shows the issue:

from PyPDF2 import PdfReader, PdfWriter

file = 'v2 - signed.pdf'

reader = PdfReader(file)
writer = PdfWriter()

writer.append(reader,[0])

writer.update_page_form_field_values(
    writer.pages[0], {'Nr':'SN230001'}
)
        
with open (file, 'wb') as stream_out:
    writer.write(stream_out)
    stream_out.close()

This is the form that is used. I just deleted personal informations from the form:
v2 - unsigned.pdf

This is the signed form:
v2 - signed.pdf

And this is the file after updating the form field:
v2 - after updating.pdf

[neversphere]

This is probably the same problem I had. I think the docs are wrong. Try appending the reader rather than just copying over a page:

reader = PdfReader(argv[0])
writer = PdfWriter()
writer.append(reader)

I have #1806 out to fix the docs.

[liam-meak]

@neversphere Thanks for the reply, I tested your suggestion and the signed signature field and radio buttons stay intact.
But this still raises another problem because now the unsigned signature field gets deleted from the form

Seems like there are still issues copying the original structure of the pdf