Large PDFs are a daily friction: email attachments bounce, upload forms reject them, and cloud storage fills up. This guide walks through the techniques that actually move the needle on PDF file size — and the ones that just waste your time.
Why PDFs get so large in the first place
Most oversized PDFs are oversized because of embedded images, redundant fonts, or unused object streams left over from the original export. A PDF that prints at 300 DPI but is only ever viewed on screen is carrying 4–10× more pixel data than it needs.
The three levers that actually shrink a PDF
Object-stream re-serialization (deduplicating shared resources), image down-sampling (re-encoding embedded images at a lower DPI), and metadata stripping (removing XMP blocks, thumbnails, and form data the recipient doesn't need). The compress-pdf tool runs all three in a single pass.
When compression hurts quality
Aggressive JPEG re-encoding can soften photos and add halos around text inside scanned PDFs. If the document is OCR'd or screenshot-heavy, prefer the lighter compression preset and check the preview before downloading.
A repeatable workflow
Run the compressor first, check the result, and if it's still too large, split the PDF and recompress the heaviest sections individually. For final delivery to print, skip compression entirely and rely on the original export.