libretero.js

const { PDFDocument, PageSizes, rgb } = require('pdf-lib');
const fs = require('fs');
const pageSize = PageSizes.Legal;
const sheetSize = PageSizes.Legal[1] / 3;
const offset = 20;

const createBox = (page) => {
  page.drawRectangle({
    x: offset,
    y: pageSize[1] - offset - (pageSize[1] - offset * 2),
    width: pageSize[0] - offset * 2,
    height: pageSize[1] - offset * 2,
    borderWidth: 1,
    borderColor: rgb(0, 0, 0),
  });

  page.drawLine({
    start: { x: offset * 4, y: pageSize[1] - offset },
    end: { x: offset * 4, y: offset },
    color: rgb(0, 0, 0),
  });
};

const createSheet = (page, number = 1) => {
  page.drawLine({
    start: { x: offset, y: pageSize[1] - offset - sheetSize * number },
    end: {
      x: pageSize[0] - offset,
      y: pageSize[1] - offset - sheetSize * number,
    },
    color: rgb(0, 0, 0),
  });

  page.drawLine({
    start: {
      x: offset,
      y: pageSize[1] - offset - sheetSize * number + sheetSize / 2,
    },
    end: {
      x: offset * 2,
      y: pageSize[1] - offset - sheetSize * number + sheetSize / 2,
    },
    color: rgb(1, 0, 0),
  });
};

/**
 * Sheets must be:
 * All margins 0.2in
 * Page Size 7in x 4.6in
 */
const embedSheet = async (pdfDoc, page, pageSource, lane = 1) => {
    if(pageSource) {
        const processedSource = await pdfDoc.embedPage(pageSource);
        page.drawPage(processedSource, {
            x: offset * 4,
            y: pageSize[1] - offset - (sheetSize * lane),
            opacity: 1,
          });
    }
}

async function createLegalSizePDF() {
  const pdfDoc = await PDFDocument.create();

  const externalPdfBytes = fs.readFileSync('input.pdf');
  const externalPdfDoc = await PDFDocument.load(externalPdfBytes);
  const externalSheets = externalPdfDoc.getPages();
  const sheetsPerPage = pageSize == PageSizes.Legal ? 3 : 2;
  const pages = Math.ceil(externalSheets.length / sheetsPerPage);

  for (let i = 0; i < pages; i++) {
    const page = pdfDoc.addPage(pageSize);
    await embedSheet(pdfDoc, page, externalSheets.shift());
    await embedSheet(pdfDoc, page, externalSheets.shift(), 2);

    if (pageSize == PageSizes.Legal) {
        await embedSheet(pdfDoc, page, externalSheets.shift(), 3);
    }

    createBox(page);
    createSheet(page);
    createSheet(page, 2);

    if (pageSize == PageSizes.Legal) {
      createSheet(page, 3);
    }
  }

  const pdfBytes = await pdfDoc.save();

  fs.writeFileSync('legal_size.pdf', pdfBytes);
}

createLegalSizePDF().catch(console.error);