January 20, 2026 · ToolDai team · pdf · privacy · engineering
Why our PDF tools run in your browser (and why that matters)
When you merge or split a PDF on ToolDai, the file never leaves your machine. Here's why that's unusual, and what it costs.
Most PDF websites work like this: you upload your file to their server, they do the work there, and send you a link to download the result. That's fine for a public document. It's not fine for a signed contract, a bank statement, or your tax return.
We built ToolDai's PDF tools to run entirely in your browser. When you drag a PDF into Merge, Split, Rotate or Reorder:
- The file is read into your browser's memory using a FileReader.
- pdf-lib — a 150 KB JavaScript library — parses, edits and re-saves the PDF locally.
- The result is handed back to you as a download. Nothing ever touches our server.
What this costs us. We can't show you ads based on your file. We can't pre-process huge documents on a beefy server. We don't have a backend fleet to pay for, but we also don't get any usage data about what you did with the file.
What this costs you. A 50 MB PDF will take longer in a browser tab than on a server with 32 cores. If your laptop is already struggling, the browser tab will struggle more. There's a 100 MB limit per file in our tools — larger PDFs will crash most browsers anyway.
What it saves you. The uncomfortable question "where did this file end up?" never comes up. If the tab is closed, the file is gone, and we never had a copy.