How PDF Compression Works
PDF compression combines structural optimization and image re-encoding. Structural optimization removes unused objects, deduplicates resources, and enables object streams. Image compression downsamples high-resolution photos embedded in the PDF and applies JPEG or JPEG2000 codecs.
Lossless vs lossy in PDFs
Text and vector art compress losslessly. Embedded photos are usually lossy — lowering quality reduces size but can introduce artifacts. Always preview output before sharing client-facing documents.
What browser tools optimize
Client-side compressors typically rebuild the PDF with object streams and may re-embed images at lower resolution. They cannot beat dedicated desktop tools on huge scanned books but are excellent for everyday office PDFs under ~50MB.