To compress a PDF without noticeable quality loss, reduce the resolution of the images inside it to a screen-friendly level (around 144 DPI) and re-encode them — this is where almost all the size lives. You can do this entirely in your browser with Compress PDF, so your document is never uploaded.
Why PDFs get so large
Most oversized PDFs are big because of embedded images — scans, screenshots, and photos saved at full camera resolution. The text and vector content is tiny by comparison. So the fastest way to shrink a PDF is to compress those images, not the text.
What 'without losing quality' really means
There's a difference between lossless (identical pixels, modest savings) and visually lossless (slightly re-encoded, but indistinguishable on screen, with large savings). For email, web upload, and reading, visually-lossless is what you want: a 20 MB scanned PDF can often drop to 2–4 MB with no visible difference at normal zoom.
How to compress a PDF privately
- Open Compress PDF and drop your file — it stays in your browser.
- It re-renders each page at a screen-friendly resolution and recompresses the images.
- Download the smaller PDF. Nothing was uploaded.
This approach works best for scanned or image-heavy PDFs. For a PDF that's mostly text, it's already small — compression won't help much, and you're better off leaving it as-is.
Tips to keep quality high
- Keep the original if you may need to reprint at high resolution later.
- If the PDF is a set of photos, consider exporting only the pages you need first with Split PDF.
- Starting from images instead? Build a right-sized PDF directly with Images to PDF.