curl --request GET \
  --url https://restapi.sign.plus/v2/envelope/{envelope_id}/documents \
  --header 'Authorization: Bearer <token>'

{
  "documents": [
    {
      "id": "<string>",
      "name": "<string>",
      "filename": "<string>",
      "page_count": 123,
      "pages": [
        {
          "width": 123,
          "height": 123
        }
      ]
    }
  ]
}