Adds one or more documents to an existing envelope. The tabs of the original document will be applied to the new document. **Note:** When adding or modifying documents for an in-process envelope, Docusign recommends locking the envelope prior to making any changes. If the file name of a document contains Unicode characters, you need to include a `Content-Disposition` header. Example: **Header:** `Content-Disposition` **Value:** `file; filename=\"name\";fileExtension=ext;documentId=1` **Note:** This method works on documents only. To add recipient or document tabs, use methods from the EnvelopeRecipientTabs resource. <ds-inlinemessage kind="warning"> If HTML document files contain <code>&lt;img&gt;</code> elements with the <code>src</code> attribute set to a path or URL, those images will not be displayed. Images in HTML files must be encoded in Base64 format, like this:<br/> <code>&lt;img src="data:image/gif;base64,R0lGODlh...IQAAOw==" alt="Base64 encoded image" width="150" height="150"/&gt;</code> </ds-inlinemessage>

{
  "success": true,
  "data": {
    "id": "abc123",
    "created_at": "2025-01-01T00:00:00Z"
  }
}

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid request parameters"
  }
}

Adds one or more documents to an existing envelope. The tabs of the original document will be applied to the new document. **Note:** When adding or modifying documents for an in-process envelope, Docusign recommends locking the envelope prior to making any changes. If the file name of a document contains Unicode characters, you need to include a `Content-Disposition` header. Example: **Header:** `Content-Disposition` **Value:** `file; filename=\"name\";fileExtension=ext;documentId=1` **Note:** This method works on documents only. To add recipient or document tabs, use methods from the EnvelopeRecipientTabs resource. <ds-inlinemessage kind="warning"> If HTML document files contain <code>&lt;img&gt;</code> elements with the <code>src</code> attribute set to a path or URL, those images will not be displayed. Images in HTML files must be encoded in Base64 format, like this:<br/> <code>&lt;img src="data:image/gif;base64,R0lGODlh...IQAAOw==" alt="Base64 encoded image" width="150" height="150"/&gt;</code> </ds-inlinemessage>

{
  "success": true,
  "data": {
    "id": "abc123",
    "created_at": "2025-01-01T00:00:00Z"
  }
}

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid request parameters"
  }
}