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.
What “without losing quality” can actually mean
Two different things. Structural savings — removing duplicated resources, unused fonts and metadata — are genuinely lossless but usually recover a modest amount. Recompressing images is where the large savings live, and it is lossy by definition. A tool advertising dramatic reduction with no quality loss at all is describing the first and delivering the second.
How to judge the result
- Open at 100% and read the smallest text on the busiest page
- Check any logo or signature for soft edges, which is where compression shows first
- If the file was already small, expect little change — there was nothing large to compress
- Never compress the same file twice; go back to the original and compress once, harder
Compression runs in your browser, so the document is never uploaded — which matters given how often the thing being compressed is a contract or a scan of an identity document.