Merge PDF
Combine multiple PDF files into a single document — drag to reorder, merge instantly in your browser.
Last updated: March 25, 2026
Used 35K+ timesWhat users say
“Merged 12 contract documents in under 30 seconds without uploading anything to a cloud service. The drag-to-reorder feature is exactly what's needed for this kind of task.”
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Buy me a coffeeWhat 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
Click "Select PDFs" or drag and drop multiple PDF files onto the upload area
Review the file order shown in the list — drag files to rearrange the merge sequence
Optionally remove any files you don't want to include by clicking the × icon
Click "Merge PDFs" to combine all files into one document
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:
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: 20Merged 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 PDFsPrivacy 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?
Will the merged PDF retain bookmarks, links, and form fields?
Can I merge password-protected PDFs?
Will the file size of the merged PDF equal the sum of the originals?
Why is my merged PDF missing some content or fonts?
Are my files sent to a server during merge?
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