[Merge PDF] #pdf #merge

mergePdf.js

// gist: https://gist.github.com/wmakeev/ede27b97b3d227258684c5e80bf7fca3

import { PDFDocument } from "pdf-lib";

/**
 * Merges pdf files in one (with pdf-lib)
 *
 * @see https://stackoverflow.com/a/68482188
 *
 * @param {ArrayBuffer[]} pdfsToMerge
 * @returns {Promise<ArrayBufferLike>}
 */
export async function mergePdfs(pdfsToMerge) {
  const mergedPdf = await PDFDocument.create();

  /** @param {ArrayBuffer} arrayBuffer */
  const createInnerPromise = async (arrayBuffer) => {
    const pdf = await PDFDocument.load(arrayBuffer);
    return await mergedPdf.copyPages(pdf, pdf.getPageIndices());
  };

  const outerPromise = pdfsToMerge.map((arrayBuffer) => {
    const innerPromise = createInnerPromise(arrayBuffer);
    return innerPromise;
  });

  const resultOuterPromise = await Promise.all(outerPromise);

  resultOuterPromise.forEach((pageArray) => {
    pageArray.forEach((page) => {
      mergedPdf.addPage(page);
    });
  });

  return (await mergedPdf.save()).buffer;
}

mergePdfsStream.js

// gist: https://gist.github.com/wmakeev/ede27b97b3d227258684c5e80bf7fca3

import { PDFDocument } from 'pdf-lib'
import _H from 'highland'
import { promiseToStream } from '@wmakeev/highland-tools'

/**
 * Merges pdf files stream in one (with pdf-lib)
 *
 * @see https://stackoverflow.com/a/68482188
 *
 * @param {Highland.Stream<ArrayBuffer>} pdfsToMerge$
 * @returns {Highland.Stream<ArrayBufferLike>}
 */
export function mergePdfsStream(pdfsToMerge$) {
  /** @type {PDFDocument} */
  let mergedPdf

  return pdfsToMerge$
    .map(async arrayBuffer => {
      if (mergedPdf === undefined) mergedPdf = await PDFDocument.create()

      const pdf = await PDFDocument.load(arrayBuffer)

      const pages = await mergedPdf.copyPages(pdf, pdf.getPageIndices())

      return pages
    })
    .map(promiseToStream)
    .flatten()
    .collect()
    .map(pages => {
      pages.forEach(p => mergedPdf.addPage(p))
    })
    .last()
    .map(async () => (await mergedPdf.save()).buffer)
    .map(promiseToStream)
    .sequence()
}