request-promise download pdf file

Add encoding: null to your request options:

const optionsStart = {
  uri: url,
  method: "GET",
  encoding: null,
  headers: {
    "Content-type": "application/pdf"
  }
};

Then, turn the response into a Buffer (if necessary):

const buffer = Buffer.from(response);

Add encoding: 'binary' to your request options:

const optionsStart = {
  uri: url,
  method: "GET",
  encoding: "binary", // it also works with encoding: null
  headers: {
    "Content-type": "application/pdf"
  }
};