How to Compress a PDF Without Making the Text Blurry
Text in a PDF only goes blurry if it was never really text. Typed text and vectors stay sharp; scanned text is a picture, and that's the part that can soften.
Two kinds of text
Real text is stored as characters and a font. It can be selected, searched and copied, and it stays sharp at any zoom. Scanned text is a photograph of printed text: a picture. Only the second kind can look blurry after compression.
Quick test: open the PDF and try to select a word. If you can, the text is real. If you can’t (or you can select only odd rectangles), you have a scan.
What Compress PDF does
Compress PDF doesn’t turn pages into pictures. It re-compresses the pictures inside the PDF and leaves text, vector graphics and fonts untouched. So for a document with real text, the text is not softened at all. For a scan, the picture has to be re-compressed, and that’s where care matters.
| Compress PDF changes | Compress PDF leaves alone |
|---|---|
| The pictures inside the file (a scan is one picture per page) | Text, vector graphics and fonts |
| File size | Page count and page sizes |
How it protects scans
- A readability floor. It never goes below 120 DPI or JPEG quality 50. In real tests at that floor, scanned text of 6.5 to 9 point stayed legible but soft; text under about 5 point can become hard to read.
- A measured guard. In Balanced and Smaller modes, it lowers quality step by step but stops early if a picture falls below a measured similarity to its source (95% and 92%). If it can’t shrink a picture by at least 8% inside the guard, it leaves it alone and says so.
- Honest targets. If you ask for a size that would need going below the floor, it gives you the best readable result and says “target not reached”, rather than a smaller file you can’t read.
- A check on the output. It re-reads the result and reports page count, page sizes and whether text is still selectable. The visual similarity shown for a PDF is an average over up to three rendered sample pages.
What to do
- Start with Balanced. It is the gentlest mode.
- Move to Smaller file only if you need to.
- Open the result and zoom to 100 to 150% on the smallest text, a signature and a stamp.
- Avoid the “Convert pages to pictures instead” option unless nothing else works. It makes text unselectable and softer.
If you can rescan, a straighter, better-lit scan compresses cleaner than a skewed one. See how to reduce the size of a scanned PDF.