PDF Tools
Merge PDF Files
Combine multiple PDFs into one file. Drag to reorder, then download instantly.
🔒 Your files never leave your device. Everything happens in your browser — no uploads, no servers, no storage.
Drop PDF files here
or click to browse — add as many as you like
Choose PDFs
Merging…
Other PDF Tools
Frequently Asked Questions
How many PDFs can I merge at once? ▾
There's no hard limit on the number of files. Practical limits depend on your device's available RAM — very large PDFs (100MB+) may be slow or cause browser memory issues on older devices. For most use cases (10–20 standard documents), merging is fast and reliable. If you hit issues, try merging in batches of 5–10 files first.
Is my data safe? Are files uploaded anywhere? ▾
Completely safe — your files never leave your device. The PDF merging happens entirely in your browser using the PDF-lib JavaScript library. Nothing is sent to any server. Unlike most online PDF tools (Smallpdf, ilovepdf, Adobe online), ToolStack processes everything locally. This means it works offline, your files stay private, and there are no size limits imposed by server policies.
Will the merged PDF retain bookmarks, hyperlinks and formatting? ▾
All page content, images, fonts and layout are fully preserved. Embedded hyperlinks within pages are retained. Document-level bookmarks (table of contents entries) may not carry over between files — this is a limitation of browser-based PDF processing. If bookmarks are critical, you'll need a desktop tool like Adobe Acrobat or PDF Arranger.
How to Merge PDF Files
Combine multiple PDF files into one document in seconds — with no upload required.
01
Add your PDF files
Click 'Choose PDFs' or drag and drop multiple PDF files onto the drop zone. You can add as many files as you need in one go.
02
Reorder your documents
Drag the file cards up and down to set the order they'll appear in the merged document. The number on each card shows the final position.
03
Check the page count
The action bar shows total files, total pages, and total file size. Make sure everything looks right before merging.
04
Click 'Merge & Download'
The tool combines all PDFs in your browser — nothing is uploaded to any server. The merged file downloads automatically when ready.
05
Verify the result
Open the downloaded PDF to confirm pages are in the right order. Rename the file from 'merged.pdf' to something descriptive.
💡 Your files never leave your device — ideal for confidential documents like contracts, financial statements, or medical records.