How to use Compress PDF
Reduce PDF file size significantly without noticeable quality loss — entirely in your browser using advanced compression algorithms. Smaller PDFs load faster, consume less storage, and stay within email attachment limits. This tool recompresses images and removes redundant metadata while preserving text crispness, vector graphics, and document structure.
- Upload your PDF by clicking or dragging it to the tool.
- Select a compression level: light (minimal quality loss), balanced, or maximum compression.
- Preview the estimated output size and quality comparison.
- Click "Compress PDF" and wait for the browser to process the file.
- Download the compressed PDF and verify the quality meets your needs.
Your data never leaves your device — 100% private processing.
What PDF compression actually does
Most PDFs contain embedded images at full resolution, even when only screen viewing is intended. Compression downsamples and re-encodes images (JPEG for photographs, PNG for graphics with transparency) at a lower quality setting. It also deduplicates identical embedded objects, strips metadata like creation timestamps and author information, removes embedded thumbnails, and applies DEFLATE or JBIG2 stream compression to content streams and font data.
Choosing the right compression level
Light compression (high quality) targets screen viewing at 150 DPI and removes only redundant metadata — file size reduction of 15–40% for typical office documents. Balanced compression resamples images to 96 DPI and applies moderate JPEG quality — typical reduction 40–70%. Maximum compression drops images to 72 DPI with aggressive JPEG encoding — 70–90% reduction, appropriate only for archiving or sharing where print quality is not required. Vector text and diagrams are never degraded by any compression mode.
Scanned vs. native PDFs
Scanned PDFs are essentially image containers — every page is a single raster image. Compression has the highest impact here, potentially shrinking a 10 MB scanned document to under 1 MB on maximum settings. Native PDFs (created by Word, LaTeX, or design tools) contain vector text which compresses differently; the file size reduction is smaller but text quality is never compromised. For scanned documents that need to remain searchable, apply OCR before compressing.
Worked examples
Scanned document
Inputs: 10 MB scanned PDF at maximum
Result: Often under 1–2 MB — varies by content
Text-heavy report
Inputs: 3 MB native PDF at balanced
Result: Modest saving — text stays sharp
PDF compression levels
| Level | Image DPI | Typical reduction | Best for |
|---|---|---|---|
| Light | ~150 DPI | 15–40% | Screen viewing, light cleanup |
| Balanced | ~96 DPI | 40–70% | Email, general sharing |
| Maximum | ~72 DPI | 70–90% | Archiving, non-print use |
Glossary
- DPI
- Dots per inch — a measure of image resolution. Higher DPI means more detail but larger file size.
- DEFLATE
- A lossless data compression algorithm used in PDF content streams to reduce file size without quality loss.
- JBIG2
- A compression standard optimized for bitonal (black and white) images, widely used for scanned documents.
- Downsampling
- Reducing the pixel resolution of an embedded image to lower file size, typically applied to photos in PDFs.
Related reading
Frequently Asked Questions
Why use Compress PDF?
- Reduces PDF file size enough to pass typical email attachment size limits
- Three compression levels let you balance image quality against storage savings
- Keeps vector text and diagrams pixel-perfect regardless of the compression level chosen
- Removes redundant embedded thumbnails and metadata without any visible change
Common use cases
- Compress a scanned property report to meet a 5 MB email attachment restriction
- Shrink a photo-heavy product brochure PDF before uploading it to a website
- Reduce a client presentation below the file-size cap imposed by a tender portal
- Downsize a high-resolution print PDF for mobile-optimized digital distribution
- Archive years of scanned receipts at lower resolution to free up cloud storage
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