How to Fill PDF Forms with Python

How to Fill PDF Forms with Python

Interactive PDF forms (AcroForm) are everywhere — contracts, applications, invoices, tax documents. Python offers several mature libraries to fill them programmatically: pypdf (successor to PyPDF2), pdfrw, and the high-level wrapper fillpdf. This guide covers all three with real-world examples.

Understanding AcroForm

PDF forms store interactive fields in the /AcroForm dictionary. Each field has:

• /T — field name (the key you use to fill it)
• /FT — field type: /Tx (text), /Btn (button/checkbox), /Ch (list/combo)
• /V — current value
• /AP — appearance stream (may need updating after changes)

Installation

pip install pypdf fillpdf pdfrw

For encrypted PDFs or advanced overlays:

pip install reportlab

Inspecting Form Fields

Before filling a form, discover what fields it contains:

from pypdf import PdfReader

def list_fields(pdf_path):
    reader = PdfReader(pdf_path)
    fields = reader.get_fields()
    if not fields:
        print("PDF has no AcroForm fields")
        return

    for name, field in fields.items():
        ftype = field.get('/FT', 'unknown')
        value = field.get('/V', '(empty)')
        print(f"Field: {name!r:40} Type: {ftype}  Value: {value}")

list_fields("form.pdf")

Typical output:

Field: 'full_name'                       Type: /Tx   Value: (empty)
Field: 'date_of_birth'                   Type: /Tx   Value: (empty)
Field: 'accept_terms'                    Type: /Btn  Value: /Off
Field: 'account_type'                    Type: /Ch   Value: (empty)

Filling with pypdf

from pypdf import PdfReader, PdfWriter
from pypdf.generic import NameObject

def fill_pdf_pypdf(input_path, output_path, data):
    reader = PdfReader(input_path)
    writer = PdfWriter()

    for page in reader.pages:
        writer.add_page(page)

    # Copy AcroForm dictionary
    if "/AcroForm" in reader.trailer["/Root"]:
        writer._root_object.update({
            NameObject("/AcroForm"): reader.trailer["/Root"]["/AcroForm"]
        })

    # Fill fields on first page
    writer.update_page_form_field_values(
        writer.pages[0],
        data,
        auto_regenerate=False
    )

    with open(output_path, "wb") as f:
        writer.write(f)
    print(f"Saved: {output_path}")

data = {
    "full_name":     "Alice Johnson",
    "date_of_birth": "03/15/1990",
    "city":          "New York",
    "email":         "alice@example.com",
}

fill_pdf_pypdf("blank_form.pdf", "filled_form.pdf", data)

Filling Multiple Pages

from pypdf import PdfReader, PdfWriter

def fill_all_pages(input_path, output_path, data):
    reader = PdfReader(input_path)
    writer = PdfWriter()

    for page in reader.pages:
        writer.add_page(page)

    for page in writer.pages:
        writer.update_page_form_field_values(page, data)

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

Checkboxes with pypdf

Checkboxes use /Yes or /Off as values:

from pypdf import PdfReader, PdfWriter
from pypdf.generic import NameObject

def set_checkbox(writer, field_name, checked=True):
    value = "/Yes" if checked else "/Off"
    for page in writer.pages:
        if "/Annots" in page:
            for annot in page["/Annots"]:
                obj = annot.get_object()
                if obj.get("/T") == field_name:
                    obj.update({NameObject("/V"): NameObject(value)})
                    obj.update({NameObject("/AS"): NameObject(value)})

reader = PdfReader("form.pdf")
writer = PdfWriter()
for page in reader.pages:
    writer.add_page(page)

set_checkbox(writer, "accept_terms",      checked=True)
set_checkbox(writer, "receive_newsletter", checked=False)

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

Filling with fillpdf (Easiest)

fillpdf is the most user-friendly option for straightforward forms:

from fillpdf import fillpdfs

# List fields
fields = fillpdfs.get_form_fields("form.pdf")
print(fields)

# Fill
data = {
    "full_name":    "Bob Smith",
    "ssn":          "123-45-6789",
    "phone":        "(555) 123-4567",
    "accept_terms": True,   # checkbox
}

fillpdfs.write_fillable_pdf(
    "form.pdf",
    "filled_form.pdf",
    data,
    flatten=False  # True = flatten to non-editable static PDF
)

Flattening the PDF

# Create a non-editable version for archiving or sending
fillpdfs.flatten_pdf("filled_form.pdf", "final_form.pdf")

Filling with pdfrw

pdfrw operates directly on the PDF tree — very fast for batch processing:

import pdfrw

ANNOT_KEY        = '/Annots'
ANNOT_FIELD_KEY  = '/T'
SUBTYPE_KEY      = '/Subtype'
WIDGET_SUBTYPE   = '/Widget'

def fill_pdf_pdfrw(input_path, output_path, data):
    template = pdfrw.PdfReader(input_path)

    for page in template.pages:
        annotations = page[ANNOT_KEY]
        if not annotations:
            continue
        for annotation in annotations:
            if annotation[SUBTYPE_KEY] == WIDGET_SUBTYPE:
                if annotation[ANNOT_FIELD_KEY]:
                    name = annotation[ANNOT_FIELD_KEY][1:-1]
                    if name in data:
                        annotation.update(
                            pdfrw.PdfDict(V=data[name], AS=data[name])
                        )

    template.Root.AcroForm.update(
        pdfrw.PdfDict(NeedAppearances=pdfrw.PdfObject('true'))
    )
    pdfrw.PdfWriter().write(output_path, template)
    print(f"Saved: {output_path}")

data = {
    "employee_name": "Carol White",
    "department":    "Engineering",
    "start_date":    "04/24/2026",
}

fill_pdf_pdfrw("contract.pdf", "signed_contract.pdf", data)

Batch Processing from CSV

Fill hundreds of forms automatically:

import csv
from fillpdf import fillpdfs
from pathlib import Path

def batch_fill(template_pdf, csv_data, output_dir):
    output_dir = Path(output_dir)
    output_dir.mkdir(exist_ok=True)

    with open(csv_data, encoding='utf-8') as f:
        reader = csv.DictReader(f)
        for i, row in enumerate(reader, 1):
            file_id   = row.get('id', f'form_{i:04d}')
            out_path  = output_dir / f"{file_id}.pdf"

            fillpdfs.write_fillable_pdf(
                str(template_pdf),
                str(out_path),
                row,
                flatten=True
            )
            print(f"[{i}] Generated: {out_path.name}")

# CSV headers: id, full_name, ssn, address, date
batch_fill("employee_form.pdf", "employees.csv", "generated_forms/")

Overlaying Text on Non-Form PDFs

If the PDF has no interactive fields, overlay text using reportlab:

from reportlab.pdfgen import canvas
from reportlab.lib.pagesizes import letter
from pypdf import PdfReader, PdfWriter
import io

def overlay_text(input_pdf, output_pdf, fields):
    """
    fields: list of (text, x, y, font_size)
    Coordinates in points (72 pts = 1 inch), origin at bottom-left
    """
    packet = io.BytesIO()
    c = canvas.Canvas(packet, pagesize=letter)

    for text, x, y, size in fields:
        c.setFont("Helvetica", size)
        c.drawString(x, y, text)

    c.save()
    packet.seek(0)

    overlay = PdfReader(packet)
    reader  = PdfReader(input_pdf)
    writer  = PdfWriter()

    for i, page in enumerate(reader.pages):
        if i < len(overlay.pages):
            page.merge_page(overlay.pages[i])
        writer.add_page(page)

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

overlay_text(
    "invoice_template.pdf",
    "invoice_filled.pdf",
    [
        ("Acme Corp LLC",    150, 680, 12),
        ("EIN: 12-3456789",  150, 665, 10),
        ("04/24/2026",       420, 720, 10),
        ("$1,250.00",        440, 580, 12),
    ]
)

Library Comparison

Troubleshooting

Fields filled but text invisible:

template.Root.AcroForm.update(
    pdfrw.PdfDict(NeedAppearances=pdfrw.PdfObject('true'))
)

Write-protected PDF:

from pypdf import PdfReader, PdfWriter

reader = PdfReader("protected.pdf")
if reader.is_encrypted:
    reader.decrypt("")  # try empty password
writer = PdfWriter()
writer.clone_reader_document_root(reader)

Dropdown selection:

from pypdf.generic import NameObject, TextStringObject

for page in writer.pages:
    if "/Annots" not in page:
        continue
    for annot in page["/Annots"]:
        obj = annot.get_object()
        if obj.get("/T") == "account_type":
            obj.update({
                NameObject("/V"):  TextStringObject("Premium"),
                NameObject("/DV"): TextStringObject("Premium"),
            })

Additional Resource

For PDF conversions (PDF→Word, PDF→image, PDF→text) without any coding, use KaijuConverter — fast, free, and no account required.

Related conversions

Document conversions that follow this topic naturally:

• PDF to DOCX
• DOCX to PDF
• MD to PDF
• HTML to PDF
• ODT to PDF
• PDF to TXT