What is PDF Merger?
PDF Merger is a free browser-based tool that combines two or more PDF files into a single document. The merging process runs entirely in your browser using PDF-lib — a JavaScript PDF engine — so your files never leave your device, even for a moment.
Merging works by reading the page structure of each PDF and writing all pages in sequence into a new output file. The original files are untouched. You can drag to reorder the files before merging, so the output pages appear in exactly the sequence you choose. Mixed page sizes (A4 and Letter in the same merge) are supported and render correctly in all major PDF readers.
Common use cases include combining separate chapters of a report into one document, merging scanned contract pages into a single signed file, assembling multi-source research documents, compiling invoice PDFs for monthly filing, and preparing multi-document submissions. There is no hard file limit — most devices handle 20+ PDFs at once without issues.
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Instant results
No server processing or wait
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100% private
Files stay on your device
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Always free
No subscription or fees
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Mobile ready
Works on any device
How to use PDF Merger
- Upload 2 or more PDF files by dragging them into the upload area
- Drag to reorder the files — pages merge in the order you set
- Click Merge — your combined PDF is processed entirely in your browser
- Download your merged PDF instantly, no server upload required
Why use OnlineToolsPlus?
PDF tools on OnlineToolsPlus use PDF-lib — a JavaScript PDF engine that runs locally in your browser. Your documents are never uploaded to a server, which means no privacy risk for sensitive contracts, financial documents or personal files. With 25+ free PDF tools covering merging, splitting, compressing, editing and converting, you have a complete PDF toolkit at no cost.
Frequently asked questions
How many PDF files can I merge at once?
You can merge as many PDFs as needed in a single operation. Add all your files, drag to set the order, and combine. The only practical limit is your device memory. For very large collections of large PDFs, processing may take longer, but there is no hard cap on the number of files.
Can I reorder pages before merging?
Yes. After adding your files, drag them into the correct order before clicking Merge. The merged PDF will combine all pages from the first file, then all pages from the second file, and so on in the order you set. For finer control over individual page ordering within a file, split the source PDF first to isolate specific pages.
Is the merged PDF the same quality as the originals?
Yes. PDF merging is a structural operation — it joins the PDF page objects without re-encoding any content. Text, images, fonts, and vector graphics retain their original quality. There is no re-rendering or compression involved in the merge itself.
Are my files uploaded to a server?
No. PDF merging runs entirely in your browser using PDF-lib, a JavaScript PDF library. No file is ever sent to any server. Your documents — which may contain sensitive personal, financial, or legal information — never leave your device.
Can I merge password-protected PDFs?
Password-protected PDFs cannot be merged until unlocked. Use the PDF Unlock tool on OnlineToolsPlus to remove the password first, then merge the unlocked files. Note: only unlock PDFs you own or have authorization to modify.
What is the maximum file size for merging?
There is no file size limit. Everything runs in your browser. Very large files (100+ MB each) may take longer to process on older devices, but will merge correctly. For best performance on large document sets, close other browser tabs to free up memory.
Can I merge PDFs with different page sizes?
Yes. The tool merges PDFs regardless of page size. If the source documents have different page sizes (A4 vs Letter, or portrait vs landscape), the merged output preserves each page at its original size. Readers like Adobe Acrobat display mixed-size PDFs correctly.
Does merging preserve hyperlinks and bookmarks?
Hyperlinks within the content (clickable URLs, internal links) are preserved. Document-level bookmarks and outlines from the source files may or may not be preserved depending on how they were created. For documents where navigation structure is critical, check the output in a PDF reader after merging.
Can I merge scanned PDFs?
Yes. Scanned PDFs are treated as image-based PDF pages and merge exactly like any other PDF. The scan quality is preserved without re-encoding. If you need the text in scanned PDFs to be searchable after merging, run the output through a PDF OCR tool first.
How is this different from combining PDFs in Adobe Acrobat?
The core merge result is identical — both join PDF page objects into a single file. The difference is cost and accessibility: Adobe Acrobat Pro costs $19–25/month, requires installation, and does not run in a browser. This tool is completely free, requires no installation, and works on any device with a modern browser, including phones and tablets.
- Check page orientation before merging. If some source PDFs are landscape and others portrait, the merged document will have inconsistent page orientations. Rotate pages using the PDF Rotate tool before merging.
- Reorder pages after merging. The tool lets you drag files to set the merge order before combining. If you need to reorder individual pages within a merged document, use the PDF Page Reorder tool.
- Compress after merging. Merging large PDFs can produce a large output file. Run the merged PDF through the PDF Compressor to reduce it for email or upload.
- Remove sensitive pages first. Use the PDF Split tool to remove unwanted pages from source documents before merging, rather than after.
Tips for Clean PDF Merging
- Job applications: Combine a resume, cover letter, and portfolio into a single PDF for clean submission.
- Legal and financial documents: Bundle contracts, supporting exhibits, and signature pages into one file for filing or email.
- Reports and presentations: Combine a title page, body report, and appendix into a single deliverable.
- Invoices and receipts: Merge multiple expense receipts into a single PDF for accounting or reimbursement requests.
- Scanned documents: When a multi-page document is scanned one page at a time, merging combines the individual page PDFs into a single coherent document.
- E-books and manuals: Combine chapter PDFs into a single publication for distribution.
Merging PDFs is one of the most frequent document tasks in professional environments:
When to Merge PDFs
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Last updated: April 11, 2026
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