const PDFMerger = require('pdf-merger-js');

var merger = new PDFMerger();

(async () => {
  await merger.add('pdf1.pdf');  //merge all pages. parameter is the path to file and filename.
  await merger.add('pdf2.pdf', 2); // merge only page 2
  await merger.add('pdf2.pdf', [1, 3]); // merge the pages 1 and 3
  await merger.add('pdf2.pdf', '4, 7, 8'); // merge the pages 4, 7 and 8
  await merger.add('pdf3.pdf', '3 to 5'); //merge pages 3 to 5 (3,4,5)
  await merger.add('pdf3.pdf', '3-5'); //merge pages 3 to 5 (3,4,5)

  await merger.save('merged.pdf'); //save under given name and reset the internal document
  
  // Export the merged PDF as a nodejs Buffer
  // const mergedPdfBuffer = await merger.saveAsBuffer();
  // fs.writeSync('merged.pdf', mergedPdfBuffer);
})();

import PDFMerger from 'pdf-merger-js/browser';
import React, { useEffect, useState } from 'react';

// files: Array of PDF File or Blob objects
const Merger = (files) => {
  const [mergedPdfUrl, setMergedPdfUrl] = useState();

  useEffect(() => {
    const render = async () => {
      const merger = new PDFMerger();

      for(const file of files) {
        await merger.add(file)
      }

      const mergedPdf = await merger.saveAsBlob();
      const url = URL.createObjectURL(mergedPdf);

      return setMergedPdfUrl(url);
    };

    render().catch((err) => {
      throw err;
    });

    () => setMergedPdfUrl({});
  }, [files, setMergedPdfUrl]);

  return !data ? (
    <>Loading</>
  ) : (
    <iframe
      height={1000}
      src={`${mergedPdfUrl}`}
      title='pdf-viewer'
      width='100%s'
    ></iframe>
  );
};

const merger = new PDFMerger();

// Add files

// Set only producer
await merger.setMetadata({
  producer: "Custom Producer",
});

// Set all 4 fields
await merger.setMetadata({
  producer: "Custom Producer",
  author: "Custom Author",
  creator: "Custom Creator",
  title: "Custom Title"
});