How We Compress PDFs
PDF compression works differently from image compression. PDFs contain multiple types of content—images, text, fonts, and vector graphics—each requiring different optimization strategies.
1. Image Downsampling
PDFs often contain high-resolution images (300+ DPI) that are overkill for screen viewing. We downsample these to an appropriate resolution based on the compression preset:
- Screen: 120 DPI (maximum compression, great for web/email)
- Ebook: 150 DPI (balanced quality and size)
- Printer: 300 DPI (suitable for home printing)
- Prepress: 300 DPI color, 1200 DPI mono (highest quality)
Note: Images already near the target DPI are skipped to avoid unnecessary reprocessing.
2. Image Recompression
Embedded images are recompressed using efficient codecs:
- JPEG images → recompressed with industry-leading encoders at optimal quality
- Uncompressed images → converted to JPEG or PNG as appropriate
- Lossless images with few colors → converted to indexed color
3. Font Optimization
Fonts are often embedded in full, even when only a few characters are used:
- Font subsetting: Keep only the characters actually used in the document
- Font compression: Apply efficient compression to embedded font data
- Font embedding: Ensure all required fonts are properly embedded for portability
4. Structure Cleanup
PDFs accumulate cruft over time, especially after editing:
- Remove unused objects and orphaned data
- Linearize for faster web loading ("Fast Web View")
- Compress object streams for smaller file size
What We Preserve
- Text — Remains sharp and searchable (not rasterized)
- Vector graphics — Lines, shapes, and charts stay crisp
- Links and bookmarks — Navigation elements work
- Page structure — Layout and formatting unchanged
- Form fields — Interactive elements remain functional
Expected Results
Compression results vary widely based on PDF content:
| PDF Type | Typical Savings |
|---|---|
| Photo-heavy PDFs | 60-80% |
| Scanned documents | 50-70% |
| Mixed content (text + images) | 30-50% |
| Text-only documents | 10-30% |
| Already optimized PDFs | 0-10% |
Multi-Page PDFs
Multi-page PDFs are processed as a single document—all pages are optimized together. This allows us to deduplicate fonts and images that appear on multiple pages, often resulting in better compression than processing pages individually.
Large PDFs (100+ pages) may take longer to process, but the compression quality is the same.