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Merge PDF

Combine multiple PDF files into one document directly in your browser. Reorder files, merge sections, and create a single PDF for submissions, archives, packets, or client deliverables.

Last updated: March 25, 2026

Client-Side Processing
Input Data Stays on Device
Instant Local Execution
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What is Merge PDF?

PDF merging combines multiple separate PDF files into a single unified document, preserving all pages, formatting, fonts, and embedded images from every source file. The result is a single PDF that can be shared, printed, or archived as one coherent unit. This is one of the most common document workflows — used daily by professionals who deal with contracts, reports, invoices, and scanned documents.

This tool merges PDFs entirely in your browser using the pdf-lib JavaScript library. Your files are never uploaded to any server — not even temporarily. You can drag and drop files to reorder them before merging, and the download begins immediately once processing is complete. There are no file count limits or watermarks added to the output.

How to Use Merge PDF

1

Click "Select PDFs" or drag and drop multiple PDF files onto the upload area

2

Review the file order shown in the list — drag files to rearrange the merge sequence

3

Optionally remove any files you don't want to include by clicking the × icon

4

Click "Merge PDFs" to combine all files into one document

5

The merged PDF downloads automatically to your device

Common Use Cases

  • Combining a main contract with all its appendices and schedules into one submission document
  • Merging monthly financial reports and bank statements for year-end accounting
  • Joining scanned document pages saved as separate PDFs into a single file
  • Combining chapters or sections of a book, manual, or course materials
  • Merging multiple invoice PDFs into one document for expense reimbursement
  • Assembling a complete job application package (resume, cover letter, certificates) as one PDF
  • Combining survey responses or form submissions exported individually
  • Joining client deliverables (designs, reports, specs) into a single delivery package

Example Input and Output

Merging a three-part document set into one submission-ready PDF:

Input files (in order)
File 1: contract-main.pdf (12 pages)
File 2: appendix-A-pricing.pdf (3 pages)
File 3: appendix-B-sla.pdf (5 pages)
Total source pages: 20
Merged PDF output
Merged file: contract-complete.pdf
Total pages: 20
File size: Combined (original sizes summed)
Page order: contract pages 1-12, then pricing 13-15, then SLA 16-20
Fonts and images: Preserved from all source files
Bookmarks: Preserved from source PDFs

How This Tool Works

Each uploaded PDF file is read as an ArrayBuffer using the FileReader API. The pdf-lib library loads each ArrayBuffer as a PDFDocument, then copies all pages from each source document into a single destination PDFDocument in sequence. The library preserves font references, image XObjects, and resource dictionaries during the copy operation. The final merged PDFDocument is serialized back to bytes and offered as a download via a Blob URL.

Technical Stack

pdf-lib (JavaScript)FileReader APIClient-side onlyNo server uploadBlob URL download

Privacy First

Your PDFs never leave your browser. All merging happens locally using pdf-lib — no files are uploaded, stored, or transmitted to our servers at any point.

Sort Before Merging

Name your files with a numeric prefix (01-intro.pdf, 02-main.pdf, 03-appendix.pdf) before selecting them — most browsers upload files in alphabetical order, which will automatically match your intended page order.

Large Files Tip

For merges totaling over 200MB, close other browser tabs to free up available memory. Chrome and Firefox allocate between 512MB and 2GB of JavaScript heap — large PDFs can exhaust this limit. For very large document sets, Adobe Acrobat or Ghostscript are more suitable.

Frequently Asked Questions

Is there a limit on how many PDFs I can merge?

There is no hard file count limit — you can merge as many PDFs as you need. However, very large merges (50+ files or hundreds of MB total) may be slow depending on your device's memory and CPU. For very large documents, merge in batches of 10-15 files.

Will the merged PDF retain bookmarks, links, and form fields?

Text content, images, fonts, and formatting are always preserved. Bookmarks (PDF outlines) and hyperlinks are preserved when present in the source files. Interactive form fields and digital signatures may be flattened (converted to static content) depending on the complexity of the source PDFs.

Can I merge password-protected PDFs?

Only if you know the password and the PDF allows merging (user permissions). You can unlock a password-protected PDF separately and then merge. This tool does not crack or bypass PDF encryption.

Will the file size of the merged PDF equal the sum of the originals?

Approximately, yes. PDF merging using pdf-lib does not re-compress content — it combines the existing content streams. Minor overhead for the combined document structure is added, but the total size should be very close to the sum of the input files. To reduce size after merging, compress the output through the PDF Compressor tool.

Why is my merged PDF missing some content or fonts?

This can happen if a source PDF is damaged, password-protected, or uses proprietary font encoding. Try opening the source file in a PDF viewer first to verify it displays correctly. If it looks correct in a viewer but fails to merge, the file may be using non-standard PDF features.

Are my files sent to a server during merge?

No. All merging is performed entirely in your browser using the pdf-lib JavaScript library. Your files never leave your device — they are processed in browser memory and the merged file is generated locally, then downloaded directly to your device.

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