Notes

<button id="mergePdfsButton">Merge PDFs</button>
<input type="file" id="pdfFilesInput" multiple accept="application/pdf">
<script>
document.getElementById('mergePdfsButton').addEventListener('click', async () => {
const pdfFilesInput = document.getElementById('pdfFilesInput');
const files = pdfFilesInput.files;

if (files.length === 0) {
alert('Please select some PDF files.');
return;
}

// Load pdf-lib
const { PDFDocument } = PDFLib;

// Create a new PDFDocument
const mergedPdf = await PDFDocument.create();

for (const file of files) {
const arrayBuffer = await file.arrayBuffer();
const pdf = await PDFDocument.load(arrayBuffer);

const copiedPages = await mergedPdf.copyPages(pdf, pdf.getPageIndices());
copiedPages.forEach((page) => mergedPdf.addPage(page));
}

// Serialize the merged PDF document to bytes (a Uint8Array)
const mergedPdfBytes = await mergedPdf.save();

// Create a blob from the bytes
const blob = new Blob([mergedPdfBytes], { type: 'application/pdf' });

// Create a link element
const link = document.createElement('a');

// Set the link element to download the merged PDF
link.href = URL.createObjectURL(blob);
link.download = 'merged.pdf';

// Append the link to the body
document.body.appendChild(link);

// Programmatically click the link to trigger the download
link.click();

// Remove the link from the document
document.body.removeChild(link);
});
</script>
<script src="https://unpkg.com/pdf-lib/dist/pdf-lib.min.js"></script>