How to make a PDF smaller without wrecking it

Most oversized PDFs are big for one reason: images. A ten-page contract that's pure text is rarely over a few hundred kilobytes. A ten-page scan, or a report full of screenshots, can easily be 20MB — because every page is really a photograph.

What compression actually does

PDF compressors work on three levers:

1. Re-encoding images. Photographs stored as PNG or uncompressed data get re-encoded as JPEG. This is where most of the savings come from, and at reasonable quality settings the difference is invisible on screen.
2. Downsampling. A page scanned at 600 DPI holds four times the pixels of the same page at 300 DPI. For reading on screen or standard printing, 150–200 DPI is plenty.
3. Structural cleanup. Removing duplicate embedded fonts, unused objects, and old versions of edited pages. Lossless, but usually a small win.

Text in a real (non-scanned) PDF is not an image, so compressing it never makes the letters fuzzy. If your compressed PDF looks blurry, it was a scan — the pictures of text were downsampled, not the text.

Hitting a hard limit

Upload forms with limits like "max 2MB" or "max 100KB" are the usual reason people need this. Two approaches, in order:

• Run the file through Compress PDF at the strongest setting that still reads clearly.
• If it's still over — usually a scan — reduce the page pixel size itself with Resize PDF, or re-scan at a lower DPI.

For a form that wants a photo under a size cap (job portals and government forms love this), compress the image before it ever goes into a PDF with Compress Image — you get finer control targeting the exact kilobyte limit.

What not to do

Don't screenshot pages and rebuild the PDF from the screenshots — you'll lose selectable text, searchability and accessibility, and the file often ends up bigger. And don't email yourself progressively smaller re-saves from a word processor; each round trip can rasterise more content.

Everything above runs in your browser on this site — the file never uploads to a server, so it's safe for contracts and IDs.