Extract and Fill Existing PDF Forms Programmatically
Extracting and filling form fields in PDFs allows you to automate working with interactive documents. Using our API’s Extract Form Fields and Fill Form Fields endpoints, you can easily retrieve editable fields from existing PDFs and populate them with dynamic data, streamlining workflows and improving efficiency.
In this tutorial, we’ll use an editable KYC (Know Your Customer) form to demonstrate how extraction and filling works.
1. Extract Form Fields
The first step is to analyze your fillable PDF to understand its structure. The Extract Form Fields endpoint takes either a file URL or a base64 string and returns a structured JSON containing all available fields. For each field you will get:
- Unique field name – used as the key when filling data.
- Field type – e.g.,
textfield,checkbox. - Current value – if the PDF already contains pre-filled data.
- Metadata – includes information such as field ID, page number, lock state, or whether a field supports multiple lines of input.
Endpoint Details
- HTTP Method:
POST - Request URL:
https://us1.pdfgeneratorapi.com/api/v4/pdfservices/form/fields - Documentation: Official API Docs
Request Body
{"file_url": "https://us1.pdfgeneratorapi.com/api/v4/documents/66/97e0434f37..."}
Response
{
"response": {
"contact_address": {
"id": "17",
"type": "textfield",
"name": "contact_address",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"country_of_birth": {
"id": "28",
"type": "textfield",
"name": "country_of_birth",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"date_of_birth": {
"id": "27",
"type": "textfield",
"name": "date_of_birth",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"document_number": {
"id": "19",
"type": "textfield",
"name": "document_number",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"email": {
"id": "30",
"type": "textfield",
"name": "email",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"first_name": {
"id": "24",
"type": "textfield",
"name": "first_name",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"identity_document": {
"id": "18",
"type": "textfield",
"name": "identity_document",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"issued_on": {
"id": "22",
"type": "textfield",
"name": "issued_on",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"issuing_country": {
"id": "21",
"type": "textfield",
"name": "issuing_country",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"last_name": {
"id": "25",
"type": "textfield",
"name": "last_name",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"nationality": {
"id": "29",
"type": "textfield",
"name": "nationality",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"other_countries": {
"id": "16",
"type": "textfield",
"name": "other_countries",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"phone": {
"id": "31",
"type": "textfield",
"name": "phone",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"pic": {
"id": "26",
"type": "textfield",
"name": "pic",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"residence_address": {
"id": "23",
"type": "textfield",
"name": "residence_address",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"tax_confirmation": {
"id": "15",
"type": "checkbox",
"name": "tax_confirmation",
"locked": false,
"pages": [
1
],
"value": true,
"default": false
},
"tax_residency": {
"id": "14",
"type": "textfield",
"name": "tax_residency",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
},
"valid_until": {
"id": "20",
"type": "textfield",
"name": "valid_until",
"locked": false,
"pages": [
1
],
"value": "\n\n",
"multiline": true
}
}
}
2. Fill Form Fields
Once you know which fields are available, you can move on to filling them with actual data. The Fill Form Fields endpoint accepts the same file URL or base64 string together with key-value pairs matching the extracted field names. In return, you receive a fully populated PDF that can be downloaded or shared immediately.
Endpoint Details
- HTTP Method:
POST - Request URL:
https://us1.pdfgeneratorapi.com/api/v4/pdfservices/form/fill - Documentation: Official API Docs
Request Body
{
"file_url": "https://us1.pdfgeneratorapi.com/api/v4/documents/66/97e0434f37...",
"data":{
"contact_address": "123 Main Street, New York, NY 10001, USA",
"country_of_birth": "United States",
"date_of_birth": "1985-07-14",
"document_number": "X1234567",
"email": "john.doe@example.com",
"first_name": "John",
"identity_document": "Passport",
"issued_on": "2015-06-01",
"issuing_country": "United States",
"last_name": "Doe",
"nationality": "American",
"other_countries": "Canada, Germany",
"phone": "+1 000 000 0000",
"pic": "123456",
"residence_address": "456 Elm Street, Los Angeles, CA 90001, USA",
"tax_confirmation": true,
"tax_residency": "United States",
"valid_until": "2025-06-01"
},
"output": "url",
"name": "KYC_Form"
}
Response
The response field contains a direct URL to the generated, filled PDF form.
{
"response": "https://us1.pdfgeneratorapi.com/api/v4/documents/66/d83e7f0104...",
"meta": {
"name": "KYC_Form.pdf",
"display_name": "KYC_Form",
"encoding": "binary",
"content-type": "application/pdf",
"public_id": "41905c77709c9b5ba42946491c8942b0"
}
}
Related articles you may find helpful
- Converting HTML to PDF - How to start?
- How to Create a Form
- Is it possible to deploy PDF Generator API on premises (on-prem) or have dedicated infrastructure?
Updated on: 10/09/2025
Thank you!