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Fill PDF forms from JSON data with JustFill and an n8n form trigger

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Created by: JustFill || justfillapp
JustFill

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Last update 2 days ago

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Quick overview

Collect an existing PDF and JSON through an n8n form, upload the binary, map named fields, fill the original layout, and return a temporary download link. For new runs, use the strict-mapping JSON linked in Setup; the catalog JSON is an older version.

How it works

  1. Triggers when a user submits an n8n form with a PDF upload and a “Data JSON” text payload.
  2. Calls the JustFill MCP API to request a one-time upload slot, then uploads the submitted PDF to the provided URL.
  3. Calls JustFill to open the uploaded PDF and retrieve its saved template field metadata.
  4. Parses the submitted JSON and matches its keys to JustFill template field names (case- and punctuation-insensitive), producing a field-ID-to-value map.
  5. Sends the mapped values to JustFill to fill the PDF and returns a temporary download URL for the generated file.
  6. Redirects the form response to the filled PDF download link.

Setup

  1. Start with the setup guide and synthetic test PDF. Import the current strict-mapping workflow JSON from the public repository. Create a JustFill account and API key; use the Config placeholder only for local tests and an n8n credential or environment variable in production.
  2. Save a JustFill template for each PDF you plan to fill (with named fields) so the workflow can map JSON keys to those field names.
  3. Use the form trigger URL in n8n with a synthetic PDF and a minimal JSON object. In the current repository version, names match exactly after case and punctuation normalization with Unicode letters preserved. Unknown keys, ambiguous names, and duplicate field targets stop before filling; arrays and nested values are rejected. Test every mapping before connecting a real data source.

Requirements

  • JustFill account and API key
  • A reviewed JustFill template with named fields for the exact PDF version
  • An n8n instance with Form Trigger, HTTP Request, and Code nodes

Customization

  • Replace the Form Trigger with Gmail, Google Drive, Dropbox, Airtable, or a webhook.
  • Move the JustFill API key from the Config node to an n8n credential or environment variable before production.
  • Extend the mapping node with aliases when source JSON keys differ from template field names.

Additional info

JustFill is built by the template author. No AI model key is required after the PDF template is reviewed and saved. Free downloads may contain a watermark; paid downloads can be clean. Links are temporary. Never publish real API keys or customer data. The repository JSON has stricter validation than this older catalog copy; use the linked current version for new runs.