How to Compress PDF Files Online
Last Updated: August 15, 2026
Large PDF files are frustrating — they bounce back from email inboxes, slow down uploads, and waste storage. Compressing a PDF reduces its file size while preserving the content and layout you need.
Why are PDFs so large?
Most PDFs are heavy because of embedded images. A single scanned page at 300 DPI can weigh 2–5 MB, and documents exported from PowerPoint or Word often embed high-resolution photos that are never viewed at full size.
What compression does
PDF compression typically works in two ways:
- Image re-encoding — photos are re-saved with optimized JPEG quality, dramatically reducing their weight.
- Lossless re-packaging — the document structure is rebuilt, removing redundant data and compressing streams.
Frequently Asked Questions
At default settings, visual quality loss is imperceptible. You can adjust quality settings for more aggressive compression.
It depends on the content. Image-heavy PDFs typically shrink 40–90%. Text-only PDFs save 5–20%.
Yes. Scanned PDFs benefit the most from compression since their size comes almost entirely from images.