Merge PDF

How to Use Merge PDF

1. Click or drag-and-drop your PDF files into the upload area.
2. Arrange the files in the desired merge order by dragging the file thumbnails.
3. Click the 'Merge' button to start combining the PDFs.
4. Wait for the process to complete, which depends on total file size and number of pages.
5. Download the merged PDF file to your device.

How It Works

This tool leverages the pdf-lib library's PDFDocument.copyPages() method to copy all pages from each source PDF into a new PDFDocument. It preserves page dimensions by maintaining the original media box settings, and keeps annotations and embedded fonts intact to ensure fidelity. The entire process is executed client-side in your browser's JavaScript engine, which means no file data is sent over the internet. Memory consumption scales with the total input size, with practical limits around 500MB, allowing merging of large documents with no fixed page count restrictions.

Example

// Input: Two PDF files - report1.pdf (10 pages), report2.pdf (5 pages)
// Output: merged_report.pdf (15 pages)

const mergedPdf = await PDFDocument.create();

const report1Bytes = await fetch('report1.pdf').then(res => res.arrayBuffer());
const report2Bytes = await fetch('report2.pdf').then(res => res.arrayBuffer());

const report1Doc = await PDFDocument.load(report1Bytes);
const report2Doc = await PDFDocument.load(report2Bytes);

const report1Pages = await mergedPdf.copyPages(report1Doc, report1Doc.getPageIndices());
report1Pages.forEach(page => mergedPdf.addPage(page));

const report2Pages = await mergedPdf.copyPages(report2Doc, report2Doc.getPageIndices());
report2Pages.forEach(page => mergedPdf.addPage(page));

const mergedPdfBytes = await mergedPdf.save();
// mergedPdfBytes contains the merged PDF data

When to Use Merge PDF

• Developers need to combine multiple PDF reports or invoices into a single file for distribution or archival.
• Designers want to merge separate PDF design drafts while preserving embedded fonts and annotations.
• SEO specialists consolidate PDF assets such as whitepapers or case studies for easier indexing and sharing.
• Students merge scanned lecture notes or research papers to create a cohesive study document.
• Anyone looking to combine multiple PDFs locally without risking data exposure to third-party servers.

For splitting merged documents afterward, consider using Split PDF. To optimize file size of the merged PDF, try the Compress PDF tool.