How to Compress a PDF Without Losing Quality
Why PDF File Size Matters
Large PDFs slow down email delivery, eat up cloud storage, and frustrate recipients on mobile. A 20 MB scanned contract can usually be compressed to under 4 MB with zero visible quality loss.
How PDF Compression Works
PDFs contain three main types of data: text (vector), images (raster), and fonts. Compression targets images — the biggest contributor to file size — by:
- Downsampling — reducing image DPI from 300 to 150 (print-quality to screen-quality)
- Re-encoding — converting PNG images inside the PDF to JPEG with optimised quality settings
- Removing metadata — stripping embedded thumbnails, XMP data, and duplicate font subsets
Text and vector content is never affected, so your typography stays pixel-perfect.
Three Compression Levels Explained
| Level | Use Case | Typical Reduction |
|---|---|---|
| Low | Archival, print | 10–30% |
| Medium | Email, sharing | 40–60% |
| High | Mobile, web | 60–80% |
Step-by-step: Compress with SynthPDF
- Click Compress PDF Free below or drag-and-drop your file
- Choose a quality level (Medium is best for most use cases)
- Click Compress — processing takes under 5 seconds for most files
- Download your compressed PDF
Common Questions
Will my text become blurry? No. Text is stored as vectors in PDF — it's never touched during compression. Only embedded images are re-sampled.
Can I compress a password-protected PDF? You'll need to unlock it first. Use our Unlock PDF tool, then compress.
What's the maximum file size? Free users can compress files up to 25 MB. Pro users up to 100 MB, Max up to 150 MB.