Unlock readonly form fields in a PDF

unlock_readonly.py

# pip install pypdf

from pypdf import PdfReader, PdfWriter
from pypdf.generic import NameObject, NumberObject
from pypdf.constants import FieldDictionaryAttributes as FA

MIN_HEIGHT = 30

reader = PdfReader("locked.pdf")

for page in reader.pages:

    if "/Annots" not in page:
        continue

    for field in page["/Annots"]:
        fo = field.get_object()
        height = fo["/Rect"][3] - fo["/Rect"][1]
        title, value = fo.get("/T"), fo.get("/V")
        print(height, title, value)

        ffbits = [FA.FfBits.DoNotScroll]
        if height > MIN_HEIGHT:
            ffbits += [FA.FfBits.Multiline]
        # Omitting FA.FfBits.ReadOnly makes field editable

        fo[NameObject("/Ff")] = NumberObject(sum(ffbits))

writer = PdfWriter(clone_from=reader)
writer.write("multiline.pdf")