A portal insists your PDF must be under 2 MB, but your file is 14 MB. Or an email bounces because an attachment exceeded the server threshold. Understanding why your PDF is large determines whether it can be shrunk substantially.
Two fundamentally different kinds of PDF
1. Text-based vector PDFs
Exported directly from Word, Google Docs, or InDesign. The characters are stored as vector glyphs and font instructions. These are already highly compact (a 50-page document is often under 1 MB). There is very little to compress unless high-resolution photos were pasted into the body.
2. Scanned image PDFs
Created by scanners, copiers, or phone cameras. Each page is a raster photograph. A ten-page scan easily reaches 30–50 MB. These compress dramatically, routinely shrinking by 70–90%.
Quick verification: Try highlighting words with your mouse cursor. If you can select individual characters, it's text-based. If your cursor drags a selection box over the whole sheet, it's a scanned photo.
How PDF compression works
For scanned documents, compression re-samples each page at a target DPI (dots per inch) and applies smooth JPEG encoding:
Open PDF Compressor Studio →| Intended Destination | Resolution (DPI) | Compression Preset |
|---|---|---|
| Screen viewing & email reading | 100–120 DPI | Maximum |
| Standard portal submission | 150 DPI | Balanced |
| Physical printing at office | 200 DPI | Light |
| Fine print contracts | 200+ DPI | Light |
Practical Reduction Tips
- Delete blank or duplicate pages: Eliminates redundant megabytes instantly.
- Crop white borders: Remove dead scanner bed margins from page edges.
- Scan in greyscale: Text documents in greyscale are a third of the weight of 24-bit full colour scans.