PDF compression explained: what actually shrinks your file

PDF compression is often confusing because there are several techniques bundled under the same word. Here's what's really happening.

Lossless structural compression Removing duplicate objects, normalizing fonts, and using object streams can shrink a file 5–25% with zero quality loss. This is what our [Compress PDF](/compress-pdf) tool does.

Image downsampling (lossy) The biggest savings — often 50% or more — come from downsampling embedded images. This is lossy: image resolution drops. It usually requires a server.

Font subsetting Embedded fonts can be huge if the full glyph set is included. Subsetting keeps only the glyphs actually used.

Which to choose - **Sharing on email or chat?** Lossless is usually enough. - **Archive of scanned documents?** Lossy downsampling delivers far bigger wins.

We're working on adding optional lossy compression for Pro users — stay tuned.