PDF Compress
PDFs get big when they’re full of scanned images, embedded photos or large fonts. This compressor re-encodes the images inside the PDF (usually the main size culprit) using JPEG or JPEG2000 at a chosen quality level, subsets embedded fonts to include only used glyphs, and removes duplicated resources. Typical savings: 40-80% on image-heavy files, 20-40% on text-heavy ones.
How compression works
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1
Upload the PDF
Any document up to common online size limits.
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2
Pick quality level
High (light compression, near-original), medium (balanced), low (maximum compression).
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3
Image re-encoding
Embedded images are recompressed at the chosen quality.
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Font subsetting
Embedded fonts keep only the glyphs actually used in the document.
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Resource deduplication
Repeated images (e.g. a logo on every page) are stored once and referenced.
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Download compressed file
Compare before/after size in the result view.
Typical compression ratios
| PDF type | Before | After (medium) | Savings |
|---|---|---|---|
| Scanned contract (300 dpi) | 25 MB | 4 MB | 84% |
| Photo-heavy catalogue | 40 MB | 12 MB | 70% |
| Mixed report (text + charts) | 8 MB | 3.5 MB | 56% |
| Text-only book | 2 MB | 1.6 MB | 20% |
| Born-digital invoice | 200 KB | 180 KB | 10% |
Born-digital PDFs (exported directly from Word, InDesign, web-to-PDF) are already fairly efficient; scanned PDFs have the most room to shrink.
Quality settings, explained
- High (minimal compression): JPEG quality 85-95, no downsampling. Looks identical to original. 10-30% savings typically.
- Medium (balanced): JPEG quality 70-80, 200 dpi image downsampling. Still looks crisp on screen; mild artefacts on close zoom.
- Low (maximum compression): JPEG quality 50-65, 150 dpi downsampling. Visible quality drop on images but text still readable. 60-85% savings on image-heavy PDFs.
What gets compressed
- Colour photographs — JPEG re-encoding with quality step.
- Line art and scans — JBIG2 or CCITT Group 4 for bitonal scans (near-lossless for black-and-white text scans).
- Embedded fonts — subsetted to used characters.
- Transparency and gradients — flattened or simplified where safe.
- Duplicated images — stored once, referenced multiple times.
What doesn’t compress
- Vector graphics. Already compact; no meaningful gains.
- Text content. Small as stored text streams already.
- Structured form fields, bookmarks, metadata. Untouched.
Tips for email and upload limits
| Target | Typical PDF limit |
|---|---|
| Gmail attachment | 25 MB |
| Outlook attachment | 20 MB |
| WhatsApp file | 100 MB |
| LinkedIn message | 20 MB |
| Most web upload forms | 10 MB (varies) |
Compressing to 5 MB or less gives comfortable margin for email and most uploads.
When not to compress
- Archival copies. Store uncompressed originals; compress only for distribution.
- Print-ready PDFs. Press files should not be re-compressed — keep them at original quality.
- Documents with legal significance. Compression can alter the visual appearance; keep an uncompressed copy of record.
Frequently Asked Questions
Text in PDFs is usually stored as actual text (glyphs), not images, so text quality is unaffected by image compression. Only if the PDF is a scan where every page is an image does text readability depend on compression level.
Medium quality is usually the sweet spot — strong size reduction (40-70%) with minimal visible quality loss. Drop to low only if medium doesn’t fit the limit.
Compression can alter pixel-level image data, which matters only in a tiny number of cases (forensic evidence, artwork reproduction). For contracts, reports and general documents, compression doesn’t affect content or signing validity.
Yes, but expect diminishing returns. Double-compressing JPEG images degrades quality further each time. Start from an uncompressed source whenever possible.
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