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Merge PDF

Merge, split, and reorder PDF pages securely

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Merge PDF files with pdf-lib — no server required

This tool uses pdf-lib (v1.17+) — an open-source, pure-JavaScript library for creating and modifying PDF files in the browser. Unlike server-side PDF mergers that upload your documents to a remote machine for assembly, pdf-lib reads your PDF byte streams locally using the browser's File API, copies each page's content stream and resource dictionary into a new PDF document, and triggers a download — all without network transmission.

What pdf-lib actually does during a merge

Each PDF file is a structured binary document containing:
    1. A cross-reference table listing the byte offsets of every object in the file
    2. Page objects referencing content streams (the actual drawing instructions)
    3. Resource dictionaries listing fonts, images, and colour spaces used on each page
When you click Merge, pdf-lib:
  1. Parses the cross-reference table of each source PDF
  2. Copies each page's content stream into a new PDFDocument object
  3. Merges the resource dictionaries (resolving conflicting font or image names)
  4. Rebuilds the cross-reference table for the combined document
  5. Serialises the result to a Uint8Array and triggers a browser download
The output is a standard PDF 1.7-compliant file that opens in Adobe Acrobat, Preview, and all modern PDF viewers.

Common use cases for PDF merging

Combining a multi-document application: Job applications often require a resume, cover letter, and portfolio in a single PDF. Merge all three here in seconds.

Assembling a report from separate sections: Different team members write different chapters as separate PDFs. Merge them into a single deliverable for the client.

Archiving multi-page scans: Flatbed scanners often save each scanned page as a separate file. Merge the pages into a single searchable document.

How to use the PDF Merger

  1. Upload your PDFs — Drop two or more files. pdf-lib parses each file's cross-reference table.
  2. Reorder — Use the arrows to arrange the merge order.
  3. Merge and download — pdf-lib assembles the combined PDF and triggers download.
💬 FAQ

FAQs about Merge PDF

Everything you might be wondering — answered.

Which library handles the PDF merging?+
pdf-lib (v1.17+), an open-source pure-JavaScript PDF library. It can read PDF 1.2–1.7 format files, copy page content streams, and assemble new documents without requiring any server-side processing or native dependencies.
Are my PDF files uploaded anywhere?+
No. pdf-lib reads the file bytes from the browser's File API and processes them entirely in memory. Nothing is transmitted to a server at any point.
Can I merge password-protected PDFs?+
pdf-lib can merge PDFs that have user-level permissions (printing restrictions, copying restrictions) but cannot decrypt PDFs that require a password to open. Remove the open password first using a dedicated PDF unlocker tool.
Is there a page or file count limit?+
There is no enforced limit. Practical limits depend on your device's RAM — merging 10 × 50-page PDFs (a few hundred MB total) works smoothly on most modern devices. Very large files may cause the browser tab to run out of memory.