Every time you upload a PDF or image to a random “free” compression site, you’re handing over the full file (sometimes including hidden metadata like GPS location, device info, and embedded text) plus your IP address and usage data.

You have no idea how long it’s stored, logged, or reused. Compression doesn’t require a server; it can run entirely in your browser.

Witty University built a simple local HTML tool that compresses PDFs and images 100% offline, nothing gets uploaded: https://university.witty.computer/product/universal-local-compressor-private-pdf-image-optimizer-runs-100-in-your-browser/

Privacy is basic hygiene.