Anvil PDF Filling API

openapi: 3.0.3
info:
  title: Anvil PDF Filling 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: []

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            unpublished (draft) version.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'

components:
  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.

  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