Both Aizen and Smallpdf let you merge, split and edit PDFs for free. The real differences are where your files are processed, whether there are daily limits, and what you pay for the extras. Here is an honest side-by-side.
Quick answer: Choose Aizen if you want your PDFs to stay on your device, no daily task cap, and no upsell for core tasks like merging and splitting. Choose Smallpdf if you need its broader paid suite — OCR, e-signatures, and integrations — and do not mind uploading your files.
At a glance
| Feature | Aizen PDF Tools | Smallpdf |
|---|---|---|
| Price | Free, unlimited | Free tier with daily limits; paid Pro |
| Where files are processed | In your browser (local) | Uploaded to Smallpdf servers |
| Privacy | Files never leave your device | Files uploaded to a third party |
| Daily task limit | None | Limited on the free tier |
| Merge / split / rotate / crop | Yes, free | Yes (counts toward free limit) |
| OCR & e-sign | Not offered | Yes (paid) |
| Sign-up | None | Prompted for continued use |
| Watermark | Never | No |
| Works offline | Yes, after first load | No |
Privacy is the deciding factor for most people
Smallpdf is an upload-based service: your PDF is sent to its servers, processed, and returned. That is convenient and reliable, but it means a third party handles your files — a genuine concern for contracts, financial statements, medical records or anything under an NDA.
Aizen is local-first: merging, splitting, rotating and cropping all run in your browser with pdf-lib and pdf.js. Your files never touch a remote server. For confidential documents, this is the safer default.
Callout: If a document is sensitive enough that you would hesitate to email it, local processing is the responsible choice. It removes the upload risk entirely.
Limits and cost
Smallpdf's free tier caps how many tasks you can run per day and nudges you toward a paid subscription. Aizen's core PDF tools have no daily limit and no paid tier for the basics — merge as many documents as you like, as often as you like, because the work happens on your own hardware.
Where Smallpdf pulls ahead is its paid feature breadth: built-in OCR (making scanned text searchable) and e-signature workflows. If those are core to your work, Smallpdf's Pro plan is worth considering.
Which should you choose?
- Pick Aizen for private, unlimited, free core PDF tasks — merging, splitting, rotating, cropping, converting — with nothing uploaded.
- Pick Smallpdf if you need OCR, e-signing or its integrations and are comfortable with uploads and a subscription.
For the everyday job of combining PDFs quickly and privately, the browser-based approach wins. Try the Aizen PDF Merger, then read the full PDF merging guide to get the workflow right.