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November 15, 2026 · 6 min read
You try to email a PDF and it bounces back: too large. It's one of the most common file frustrations there is. The fix is PDF compression — and the secret to doing it well is understanding that, almost always, it's the images inside the PDF that make it heavy. Here's how it works.
A PDF that's mostly text is usually small, because text is compact to store. What blows up the file size is embedded images: scanned pages, photos, high-resolution graphics, and screenshots. A single full-resolution photo can add several megabytes on its own.
So the biggest lever in shrinking a PDF is compressing and downsizing the images it contains — exactly the same principle as optimising images for the web.
PDF compression reduces file size mainly by re-compressing the embedded images at a lower quality and, often, a lower resolution. A scan stored at 600 DPI, for instance, can usually drop to 150 DPI and still look perfectly sharp on screen and in print at normal sizes.
Good compression leaves the text untouched — it stays crisp and selectable — and focuses the savings on the images, where they're barely noticeable.
It depends entirely on what's inside. A PDF full of high-resolution scans or photos can often be reduced by 70–90%, turning a 20 MB file into a couple of megabytes. A PDF that's already mostly text won't shrink much, because there wasn't much image data to compress in the first place.
For emailing, aim to get under the common 10–25 MB attachment limits; for uploading to forms, check the specific size cap.
Drop your PDF into our compressor and it re-compresses the embedded images to bring the file size down, while keeping the text sharp. Everything runs in your browser, so a confidential contract, invoice or scan is never uploaded to a server.
If your PDF is still too big after compression, consider splitting it into smaller files, or removing pages you don't need — both are quick ways to get under a stubborn size limit.