Compress PDF files online for free with our PDF Compressor. Reduce PDF file size by up to 90% using stream re-quantization, customizable image DPI scaling, and object stream compaction directly inside client browser RAM.
Upload a large PDF file needing file size reduction into browser memory.
Select target compression quality levels to optimize vector streams and image DPI.
Click Compress PDF to reduce file byte size and download your optimized document.
Optimizes embedded image XObject streams using custom DPI resolution scaling and JPEG compression quality factors.
Bundles uncompressed catalog objects into compressed FlateDecode streams for maximum document byte reduction.
All canvas rendering and stream modifications execute inside client browser memory. Zero files leave your device.
PDF document compression combines image XObject stream re-quantization with catalog object stream compaction. PDF.js renders page viewports to HTML5 Canvas contexts at a target DPI scale factor (scale = DPI / 96), re-encoding image streams with tuned JPEG quality multipliers.
The re-encoded image XObjects are embedded into a fresh document tree using pdfDoc.embedJpg(). Enabling useObjectStreams: true groups loose catalog objects into compressed FlateDecode object streams (/ObjStm), eliminating overhead from cross-reference tables.
Because processing occurs entirely inside client browser RAM via Web Workers and ArrayBuffers, compressed files generate instantly with zero network bandwidth consumption or data privacy risks.