Modify a pre-signed TriNet HSA Contribution form with today's date and a dollar amount

hsa_pdf_creator.py

#!/usr/bin/env python3

import argparse
from datetime import date

from PyPDF2 import PdfFileReader, PdfFileWriter
from PyPDF2.generic import BooleanObject, NameObject, IndirectObject

def setup_args():
    parser = argparse.ArgumentParser(description="Modify a PDF's fields for HSA contribution changes.")
    parser.add_argument("-i", "--input", help="The input PDF file.", required=True)
    parser.add_argument("-o", "--output", help="The output PDF file.", required=True)
    parser.add_argument("-a", "--amount", help="The amount of the HSA contribution.", required=True)   
    return parser.parse_args()


def set_need_appearances_writer(writer: PdfFileWriter) -> PdfFileWriter:
    catalog = writer._root_object
    if "/AcroForm" not in catalog:
        writer._root_object.update({
            NameObject("/AcroForm"): IndirectObject(len(writer._objects), 0, writer)
        })
    need_appearances = NameObject("/NeedAppearances")
    writer._root_object["/AcroForm"][need_appearances] = BooleanObject(True)

    return writer

def init_reader(infile: str) -> PdfFileReader:
    reader = PdfFileReader(infile, strict=False)
    if "/AcroForm" in reader.trailer["/Root"]:
        reader.trailer["/Root"]["/AcroForm"].update({
            NameObject("/NeedAppearances"): BooleanObject(True)
        })

    return reader


def init_writer() -> PdfFileWriter:
    writer = PdfFileWriter()
    set_need_appearances_writer(writer)
    if "/AcroForm" in writer._root_object:
        writer._root_object["/AcroForm"].update({
            NameObject("/NeedAppearances"): BooleanObject(True)
        })

    return writer


if __name__ == "__main__":
    args = setup_args()

    field_dict = {
        "12": args.amount,
        "14": date.today().isoformat()
    }

    reader = init_reader(args.input)
    writer = init_writer()

    writer.addPage(reader.getPage(0))
    writer.updatePageFormFieldValues(writer.getPage(0), field_dict)

    with open(args.output, "wb") as f:
        writer.write(f)