PDF GUIDE
How to Compress a PDF Without Losing Too Much Quality
Compressing a PDF is a trade-off. Smaller files are easier to email, upload and store, but aggressive compression can make photographs, diagrams and fine text look worse. The goal is to find the setting that gives you a small enough file while keeping the document usable.
What actually makes a PDF large?
A PDF can contain text, fonts, vector graphics, photographs and scanned page images. In most large PDFs, the bulk of the file size comes from images rather than text. If a PDF contains high-resolution photographs or scanned pages, there is usually room to reduce it. If it is mostly text and vector graphics, it may already be compact.
QuakeStar compression presets
QuakeStar's PDF Compressor uses Ghostscript quality presets. Each preset tells the compressor how aggressively to optimize images and other resources inside the PDF.
- Screen / smallest file — lowest resolution, smallest file. Best for on-screen viewing when quality is less critical.
- Ebook / balanced — a middle setting. Often a good starting point.
- Printer / high quality — higher resolution images. Larger file, better detail.
- Prepress / maximum quality — minimal compression. Closest to the original appearance.
- Default — lets Ghostscript choose its own defaults.
Real test results
We created a four-page test PDF containing scanned text pages and a photograph, then compressed it with each QuakeStar preset. These are actual measurements from QuakeStar's compressor.
| Preset | Result size | Reduction |
|---|---|---|
| Original | 5.14 MB | — |
| Screen / smallest file | 2.76 MB | 46.2% |
| Ebook / balanced | 2.76 MB | 46.2% |
| Printer / high quality | 3.18 MB | 38.2% |
| Prepress / maximum quality | 4.52 MB | 12.1% |
| Default | 2.72 MB | 47.0% |
For this particular document, the Default preset gave the smallest file, while Prepress kept the most detail. Your results will depend on what is inside your PDF.
How to choose a preset
- For email or web viewing: start with Ebook or Default. Inspect the result before sending.
- For documents with photographs: try Printer first, then move to Ebook only if the file is still too large.
- For scanned documents: scans often compress very well, but aggressive settings can blur fine text. Check the result at 100% zoom.
- For printing or archival: use Prepress or keep the original.
Always inspect the result
Before deleting the original or sending the compressed file, open it and check:
- photographs and screenshots;
- fine text and signatures;
- diagrams, charts and lines;
- scanned pages at full zoom;
- any pages you intend to print.
If something looks worse than you need, go back one preset and try again. Compression is not reversible, so keep your original for anything important.