About PDF Compressor
Powerful PDF compression using Ghostscript WebAssembly, running entirely in your browser.
🐕
Why Nobu Tools?
Nobu is my dog, and the inspiration behind these tools. Life is short, so we should spend less time on tedious tasks and more time with the ones we love.
Nobu Tools are built to save you time. Fast, private, no-nonsense utilities that just work, so you can get back to what matters.
🔧 How It Works
PDF Compressor uses Ghostscript, the industry-standard PDF processing library,
compiled to WebAssembly (WASM). This means the full power of Ghostscript runs
directly in your browser — no server required.
Vector-Preserving Compression
Unlike simple image-based compressors that rasterize your PDF (making text look like a scanned
document), Ghostscript performs intelligent compression:
- Text and fonts remain as searchable, scalable vectors
- Vector graphics (logos, diagrams, charts) stay crisp at any zoom level
- Only embedded images are recompressed and downsampled
- PDF structure and metadata are optimized
Quality Presets Explained
📱 Screen (72 DPI)
Maximum compression. Images downsampled to 72 DPI. Best for email attachments and on-screen viewing only.
📚 eBook (150 DPI)
Great balance of quality and size. Images at 150 DPI. Perfect for digital documents and ebooks.
🖨️ Printer (300 DPI)
High quality output. Images at 300 DPI. Suitable for home and office printing.
🎨 Prepress (300+ DPI)
Maximum quality. Color preservation. For professional printing and prepress workflows.
🔒 Privacy & Security
Your documents never leave your device. Here's why that matters:
- No uploads – The ~18MB Ghostscript engine downloads once and runs locally
- No server processing – Everything happens in your browser's memory
- No data collection – We can't see your files because they never reach us
- Works offline – After the engine loads, you can compress PDFs without internet
This makes PDF Compressor ideal for sensitive documents like financial statements,
legal contracts, medical records, or any confidential business files.
💡 Tips for Best Results
Which quality level should I choose?
For most use cases, eBook (150 DPI) is the sweet spot. It significantly
reduces file size while maintaining good readability. Use Screen for maximum compression
when quality isn't critical, or Printer/Prepress when you need professional output.
Why did my file size increase?
If your PDF is already well-optimized or contains mostly text with few images,
Ghostscript may actually increase the file size slightly. This is normal — the
tool works best on PDFs with uncompressed or poorly compressed images.
Why is the first compression slow?
The Ghostscript WASM engine is approximately 18MB. It downloads and initializes
the first time you use the tool. Subsequent compressions are much faster since
the engine stays in memory.
What file sizes can I compress?
The tool can handle most typical PDF sizes (up to ~100MB), but very large files
may take longer to process and consume significant browser memory. For extremely
large files, you may want to split them first using PDF Companion.
🛠️ Technical Details
PDF Compressor is powered by the following open-source projects:
- Ghostscript – The PDF/PostScript interpreter (AGPL-3.0 license)
- ghostscript-wasm – Ghostscript compiled to WebAssembly by jsscheller
- JSZip – JavaScript library for creating ZIP files (MIT license)
- Emscripten – The compiler toolchain that makes WASM possible
The compression command used is equivalent to:
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
-dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH \
-sOutputFile=output.pdf input.pdf
⚖️ License
This tool uses the following open-source components:
- Ghostscript – Released under the GNU Affero General Public License v3.0 (AGPL-3.0)
- ghostscript-wasm – Also released under AGPL-3.0 by jsscheller
- JSZip – Released under the MIT License by Stuart Knightley
The AGPL-3.0 is a copyleft license that requires derivative works to also be open source.
The Nobu Tools web interface and CSS are separate from the Ghostscript engine.
View AGPL-3.0 License Summary
Permissions: Commercial use, modification, distribution, patent use, private use
Conditions: License and copyright notice, state changes, disclose source, same license, network use is distribution
Limitations: Liability, warranty
Full license text: gnu.org/licenses/agpl-3.0