Anvil Fill API

openapi: 3.0.3
info:
  title: Anvil PDF Filling Fill API
  description: Fill existing PDF templates with JSON data. Send structured data to a PDF template and receive a filled PDF document. Supports text, checkboxes, signatures, and other form fields. Returns a binary PDF stream.
  version: 1.0.0
  contact:
    name: Anvil Support
    url: https://www.useanvil.com/docs/
  license:
    name: Proprietary
    url: https://www.useanvil.com/terms/
servers:
- url: https://app.useanvil.com
  description: Anvil production server
security:
- basicAuth: []
tags:
- name: Fill
paths:
  /api/v1/fill/{pdfTemplateID}.pdf:
    post:
      operationId: fillPdf
      summary: Fill a PDF template with data
      description: Fill an existing PDF template with JSON data. The template must be created in the Anvil app. Provide the template ID in the path and supply field data in the request body. Returns binary PDF bytes on success.
      parameters:
      - name: pdfTemplateID
        in: path
        required: true
        description: The unique identifier of the PDF template to fill.
        schema:
          type: string
      - name: versionNumber
        in: query
        required: false
        description: Version number of the template to fill. Use -1 to fill the unpublished (draft) version.
        schema:
          type: integer
          default: -1
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/FillPdfRequest'
            example:
              title: My Filled Document
              fontSize: 10
              textColor: '#333333'
              data:
                name: Jane Smith
                date: '2026-06-13'
                signature: Jane Smith
          multipart/form-data:
            schema:
              $ref: '#/components/schemas/FillPdfRequest'
      responses:
        '200':
          description: Binary PDF bytes of the filled document.
          content:
            application/pdf:
              schema:
                type: string
                format: binary
        '400':
          description: Validation error in the request.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
        '401':
          description: Missing or invalid API key.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
        '404':
          description: Template not found.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
        '429':
          description: Rate limit exceeded.
          headers:
            Retry-After:
              description: Seconds to wait before retrying.
              schema:
                type: integer
            X-RateLimit-Limit:
              schema:
                type: integer
            X-RateLimit-Remaining:
              schema:
                type: integer
            X-RateLimit-Reset:
              schema:
                type: integer
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
      tags:
      - Fill
components:
  schemas:
    FillPdfRequest:
      type: object
      properties:
        title:
          type: string
          description: Optional title to encode into the PDF document metadata.
        fontFamily:
          type: string
          description: Font family to use for text fields. Default is Noto Sans.
          default: Noto Sans
        fontSize:
          type: integer
          description: Font size for text fields in points.
          default: 10
          minimum: 1
          maximum: 100
        textColor:
          type: string
          description: Hex color code (6 digits) for text fields.
          pattern: ^#[0-9A-Fa-f]{6}$
          example: '#3E3E57'
        alignment:
          type: string
          description: Text alignment for text fields.
          enum:
          - left
          - center
          - right
          default: left
        fontWeight:
          type: string
          description: Font weight for text fields.
          enum:
          - normal
          - bold
          - italic
          - boldItalic
          default: normal
        useInteractiveFields:
          type: boolean
          description: When true, preserves interactive/fillable fields in the output PDF rather than flattening them.
          default: false
        defaultReadOnly:
          type: boolean
          description: When true, all fields are set as read-only in the output PDF.
          default: false
        data:
          oneOf:
          - type: object
            description: Key-value pairs where keys are field aliases from the template and values are the data to fill. Fields not specified will be ignored.
            additionalProperties: true
          - type: array
            description: Array of data objects for multi-page or multi-section filling.
            items:
              type: object
              additionalProperties: true
    ErrorResponse:
      type: object
      properties:
        name:
          type: string
          description: Error type name.
          example: ValidationError
        message:
          type: string
          description: Human-readable error message.
        fields:
          type: array
          description: Field-level validation errors.
          items:
            type: object
            properties:
              message:
                type: string
              property:
                type: string
  securitySchemes:
    basicAuth:
      type: http
      scheme: basic
      description: HTTP Basic Auth using your Anvil API key as the username and an empty string as the password.