code: func (r Billing_Invoice) GetPdfFileSize() (resp int, err error) {
  	err = r.Session.DoRequest("SoftLayer_Billing_Invoice", "getPdfFileSize", nil, &r.Options, &resp)
  	return
  }
docs: // Retrieve the size of a PDF record of a SoftLayer invoice. SoftLayer keeps PDF records of all closed invoices for customer retrieval from the portal and API.