const fse = require('fs-extra');
const puppeteer = require('puppeteer');
const getPdf = (page) => {
    let url = await page.url();
    return page.evaluate(url => {
        return new Promise(async resolve => {
            const reader = new FileReader();
            const response = await window.fetch(url, {
                credentials: 'same-origin',
                method: 'POST'
            });
            const data = await response.blob();
            reader.readAsBinaryString(data);
            reader.onload = () => resolve(reader.result);
            reader.onerror = () => reject('Error occurred while reading binary string');
        });
    }, url);
}

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('PDF URL', {waitUntil: 'networkidle2'});
  const pdfString = await getPdf(page);
  const pdfData = Buffer.from(pdfString, 'binary');
  fse.writeFileSync('./sample.pdf', pdfData);
  await browser.close();
})();