How PDFelly Works
Everything runs in your browser
PDFelly is built on web technologies that let powerful PDF processing happen entirely on your device. When you open a tool and select a file, the file is read into your browser's memory — never sent anywhere. All the work happens locally, then you download the result.
The technology
Our tools are powered by well-established open-source libraries:
- pdf-lib — creates and modifies PDF structure (merge, split, rotate, watermark, and more)
- pdf.js — Mozilla's engine for rendering and reading PDF pages
- Tesseract.js — optical character recognition for the OCR tool
- Canvas API — the browser's built-in image processing, used for compression and conversion
How compression works
Smart compression scans your PDF for embedded images and re-encodes them at a lower quality and resolution, while keeping all text and vector graphics untouched and searchable. It also removes duplicate images and strips unnecessary metadata. Rasterize mode instead converts each page into a single compressed image — ideal for scanned documents where the entire page is already an image.
Our compression engine carefully avoids common pitfalls: it skips CMYK images (which can be corrupted by naive re-encoding), preserves transparency masks, and validates that the output is actually smaller than the input — so you never end up with a bigger file.
Why privacy matters here
Most online PDF tools upload your files to their servers for processing. For confidential contracts, medical records, financial statements, or personal documents, that means trusting a third party with sensitive data. PDFelly removes that risk entirely — your files physically cannot leave your device because there's no upload step.
Honest limitations
Running in a browser has trade-offs. We can't match server-based tools on every feature — Office document conversion (Word/Excel/PowerPoint) needs a rendering engine too large for the browser, and some advanced compression formats (like JBIG2) aren't available client-side. We're upfront about what each tool can and can't do, rather than over-promising.