Compress PDF Files Online — Private and Free

Why PDFs get so large — and what compression actually does to them

PDFs balloon in size for a few different reasons. The most common culprit is embedded images — a PDF exported from Word with a few inserted photos can easily be 10–20MB because Office embeds images at full resolution with minimal compression. PDFs from design software like InDesign or Affinity Publisher are typically even heavier, since they embed high-resolution print-ready images throughout.

Beyond images, PDFs accumulate weight from embedded fonts (the full font file, not just the characters used), document metadata, edit history, revision data from collaborative editing, embedded colour profiles, and redundant PDF object streams created during repeated saves. A PDF that's been passed around a team and saved multiple times by different people will often be 30–40% larger than it needs to be just from accumulated overhead.

This tool addresses all of that: it uses pdf-lib to reload the PDF structure, strips unnecessary metadata and revision history, re-optimises the object streams, and optionally recompresses embedded image data. The result is a smaller file that displays and prints identically to the original for everyday reading purposes.

When you'll see the biggest reduction

PDFs with many embedded photos — product catalogues, annual reports, photo books, real estate brochures — typically see the largest reductions, often 50–70% smaller. Text-heavy PDFs with minimal graphics (legal contracts, academic papers, plain reports) will see more modest reductions of 10–25%, mostly from metadata and stream cleanup. Scanned PDFs that are essentially just a series of images will compress significantly if scanned at high DPI.

Common questions