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PDF Compression

PDF compression reduces the file size of a PDF document by re-encoding images, removing unused objects, and applying compression algorithms to preserve quality while minimizing bytes.

Why PDFs get big

A PDF's size is usually driven by three things:

  • Images — especially high-resolution photos and scanned pages (often 95%+ of the file size)
  • Embedded fonts — full font files for each typeface used
  • Object overhead — form fields, annotations, metadata, old revision history

Lossy vs lossless compression

  • Lossy compression — discards some data to shrink the file. Typically applied to photos (JPEG recompression). Quality degrades visibly at high ratios but is fine for most documents.
  • Lossless compression — preserves every byte perfectly. Used for text, line art, and when any quality loss is unacceptable. Typically saves 10-40%.

Modern PDF compressors use both: lossy for photos, lossless for text and structure. The result: a 50 MB scan can become 3 MB without visible quality loss.

What compression tools actually do

  1. Downsample images — reduce resolution from 600 dpi to 150 dpi if appropriate
  2. Re-encode photos — convert to JPEG with quality settings (Q75 typical)
  3. Convert to JBIG2 — specialized format for scanned black-and-white pages
  4. Subset fonts — keep only the glyphs actually used
  5. Remove unused objects — old form data, page thumbnails, incremental updates
  6. Recompress streams — Flate/Deflate compression on text and structure
  7. Strip metadata — optional, removes creation history and revision tracking

Typical size reductions

  • Scanned documents — 60-90% smaller (biggest gains)
  • Photo-heavy PDFs — 40-80% smaller
  • Text-only documents — 5-15% smaller (already efficient)
  • Already-compressed PDFs — minimal gain, sometimes negative

Target sizes for common use cases

  • Email attachment — under 25 MB (Gmail limit)
  • Job application — under 5 MB (most job portals)
  • Government form — under 2 MB (many gov portals)
  • Web upload — under 1 MB for fast loading

When NOT to compress

  • Legal evidence where every pixel matters
  • Medical imaging (radiology scans require lossless)
  • Archival documents stored as PDF/A
  • Already-small files (minimal benefit, possible quality loss)
Try it yourself

Compress PDF files — up to 80% smaller

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