About BunkerPDF
BunkerPDF is a set of 21 PDF tools that run entirely inside your browser. No file you open with them is ever uploaded.
Why this exists
The established free PDF sites all work the same way: you upload your document to their servers, they process it there, and they promise to delete it after a few hours. For a holiday itinerary that is fine. For a signed contract, a payslip, a medical letter or a bank statement, it means handing a copy of something private to a company you know nothing about, in exchange for rotating a page.
That trade stopped being necessary some years ago. Browsers can now run the same document libraries that desktop software uses, at close to native speed, through WebAssembly. There is no longer any technical reason for your file to leave your machine in order to be merged, split or compressed — the only reason it still does on most sites is that server-side processing is how those sites were originally built.
How it works
When you select a file, your browser hands this page a reference to it on your disk. The page reads the bytes into its own memory, rewrites them, and produces a new file for you to save. Everything happens in the tab. Three open-source libraries do the heavy lifting:
- pdf-lib reads and rewrites PDF structure — pages, rotation, text stamping and AES-256 encryption.
- pdf.js, the PDF engine built into Firefox, renders pages for the thumbnails you see and for image conversion.
- qpdf, compiled to WebAssembly, handles lossless decryption and structural optimisation.
What this means in practice
- There is no upload wait and no server queue — speed is your device’s speed.
- There is no file size limit set by us. The limit is your browser’s memory, which on a desktop is typically a few hundred megabytes.
- Once a tool page has loaded, it keeps working with no internet connection.
- There is nothing to delete afterwards, no retention window to trust, and no breach that could expose your documents.
The honest limitations
Running locally is not free of trade-offs, and it would be strange to claim otherwise:
- A very large file can exhaust a browser tab’s memory, particularly on a phone. A server with tens of gigabytes of RAM would not blink at the same document.
- Conversions to and from Word, Excel and PowerPoint are not offered here. Doing those properly requires an office suite, which cannot realistically run in a browser tab — and a poor conversion is worse than none.
- Compression cannot match a full print-production toolchain. It re-encodes images and rebuilds the file structure, which covers most of the gap, but not all of it.
How it stays free
Because nothing runs on a server, these tools cost essentially nothing to operate no matter how many people use them. There is no processing bill that grows with traffic, which is what normally forces free PDF sites into subscriptions and file limits. Hosting is inexpensive enough to cover directly.