Why Are PDF Files So Large?
PDF documents frequently reach sizes of 20MB to 100MB+ due to three main causes:
- Uncompressed High-DPI Bitmap Images: Modern digital scanners and smartphone cameras embed uncompressed raw images at 600+ DPI.
- Full Font Duplication: Multiple fonts embedded in full rather than subsetting only the characters actually used in the document.
- Redundant Metadata & Layer Objects: Hidden revision history, XML metadata packets, and orphaned vector paths from graphic design suites.
Choosing the Right Compression Ratio
When compressing PDFs for online portals or email attachments, selecting the appropriate compression algorithm is essential:
- Recommended / Balanced (Medium): Reduces DPI to 150 (perfect for screens and standard desktop printing) and yields 60-80% file size reduction.
- Extreme Compression (Low Quality): Strips all non-essential metadata, applies Flate encoding, and compresses images to 72-96 DPI. Best for archiving thousands of pages.
- High Quality / Light: Removes duplicate font objects and cleans metadata without touching image resolution.
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