What actually makes a PDF large
A PDF’s size usually comes from one of two things: images (scans, photos, screenshots) or structure and metadata (fonts, objects, and overhead). Knowing which applies to your file tells you how much it can realistically shrink.
Text-heavy PDFs (reports, contracts, exported documents) are mostly structure, so they often compress noticeably. Image-heavy or scanned PDFs are mostly pixels — and pixels can only shrink if you reduce image quality.
Lossless vs. lossy compression
Lossless compression removes unused data and compresses the PDF’s internal structure without touching the content — quality is identical, but the savings are modest on image-heavy files.
Lossy compression re-encodes images at lower quality to save more space. It shrinks scans dramatically but makes them visibly softer, and it’s heavy to do in a browser.
If your priority is keeping quality perfect, you want lossless — and you should expect bigger savings on text PDFs than on scans.
Compress a PDF in your browser, privately
1. Open the Compress PDF tool. 2. Add your PDF — it’s read on your device, never uploaded. 3. Click Compress. 4. Save the smaller file.
The tool uses lossless optimization, so quality is untouched. If a file can’t be made meaningfully smaller, the original is kept — you’ll never end up with a bigger file.
If your PDF barely shrank
That almost always means it’s image-heavy or a scan — its size lives in the pixels, which lossless compression can’t reduce without hurting quality. Options: re-scan at a lower DPI, or export the source document to PDF again at a smaller size.
Compress your PDF privately, with no quality loss.
Open the tool →