I have a simple script that should fill AcroForms inside a PDF file.

import fitz  # PyMuPDF


def fill_pdf_form(input_pdf, output_pdf, data):
    doc = fitz.open(input_pdf)

    for page_num in range(len(doc)):
        page = doc.load_page(page_num)
        for widget in page.widgets():
            field_name = widget.field_name
            print("fieldName: ", field_name)
            if field_name in data:
                widget.field_value = data[field_name]
                print("fieldValue1: ", data[field_name])
                print("fieldValue2: ", widget.field_value)

    doc.save(output_pdf, use_objstms=1)
    doc.close()


if __name__ == "__main__":
    input_pdf = "file.pdf"
    output_pdf = "file_filled.pdf"
    data = {
        "field_01": "123456 _ggtl",
        "field_multiline_01": "lorem Ipsumnnext linenagain a line",
    }
    fill_pdf_form(input_pdf, output_pdf, data)
    print(f"success: {output_pdf}")

fieldValue1 and fieldValue2 are OK on output line. But the saved PDF has no values ​​in the form fields.

What do you have to do to ensure that the set values ​​are included in the output PDF?