How to Compress a PDF Without Making the Images Look Bad

A PDF full of nothing but typed text is almost always small — a few hundred kilobytes, even for a long document. The files that balloon to tens or hundreds of megabytes are almost always the ones with embedded images: scanned pages, screenshots, or photos placed into a report. Knowing that changes how you should think about compressing a PDF, because it means the compression tool's real job is deciding how much to shrink those images, not the text.

Where the file size actually comes from

A photo taken on a modern phone camera is often 3,000-4,000 pixels wide. A page in a PDF, printed or viewed on screen, rarely needs more than 150-300 pixels per inch to look sharp — for a standard letter-size page, that's around 1,275-2,550 pixels wide. Anything beyond that is resolution the document doesn't need and the reader can't see, but it still takes up space in the file. Compression tools work by downsampling embedded images to a more reasonable resolution and re-encoding them at a chosen quality level, which is why compression can shrink an image-heavy PDF by 80-90% with no visible difference — and why the same tool barely shrinks a text-only PDF at all.

The tradeoff to watch for

Push the compression too aggressively and it becomes visible: JPEG-style blocking artifacts around text in scanned pages, softened detail in photos, banding in gradients. This matters more for documents that will be printed or zoomed into than ones only read on a screen at normal size.

Picking the right setting

Our Compress PDF tool offers multiple quality levels rather than a single one-size-fits-all setting. For a document with photos or scanned pages that need to stay print-quality, the recommended or medium setting is usually the right call — it captures most of the size reduction without visible artifacts. Reach for maximum compression only when file size is the overriding constraint (an email attachment limit, a strict upload cap) and some visible softening in images is an acceptable tradeoff.