curl --request GET \
  --url https://app.pennylane.com/api/external/v2/commercial_documents/{id} \
  --header 'Authorization: Bearer <token>'

{
  "id": 42,
  "label": "Commercial document label",
  "document_number": "PLERYGTXYOIMZZ",
  "document_type": "proforma",
  "currency": "EUR",
  "amount": "230.32",
  "currency_amount": "230.32",
  "currency_amount_before_tax": "196.32",
  "exchange_rate": "1.0",
  "date": "2020-01-01",
  "deadline": "2020-12-31",
  "currency_tax": "34.0",
  "tax": "34.0",
  "language": "fr_FR",
  "discount": {
    "type": "absolute",
    "value": "25"
  },
  "public_file_url": "https://app.pennylane.com/.../file.pdf",
  "filename": "my_file.pdf",
  "special_mention": "Additional details",
  "customer": {
    "id": 42,
    "url": "https://app.pennylane.com/api/external/v2/customers/42"
  },
  "invoice_line_sections": {
    "url": "https://app.pennylane.com/api/external/v2/commercial_documents/42/invoice_line_sections"
  },
  "invoice_lines": {
    "url": "https://app.pennylane.com/api/external/v2/commercial_documents/42/invoice_lines"
  },
  "quote": {
    "id": 201,
    "url": "https://app.pennylane.com/api/external/v2/quotes/201"
  },
  "pdf_invoice_free_text": "Document details",
  "pdf_invoice_subject": "Document subject",
  "pdf_description": "Document description",
  "commercial_document_template": {
    "id": 123
  },
  "appendices": {
    "url": "https://app.pennylane.com/api/external/v2/commercial_documents/42/appendices"
  },
  "external_reference": "FR123",
  "archived_at": "2023-08-30T10:08:08.146343Z",
  "created_at": "2023-08-30T10:08:08.146343Z",
  "updated_at": "2023-08-30T10:08:08.146343Z"
}