How to Compress a PDF Without Losing Quality

Open a PDF compressor, drop in your file, pick a quality level and download the result. That works for most files in under a minute. What the compressor actually does matters more than which one you pick: nearly all PDF size comes from embedded photos and scanned pages, so a tool that recompresses those images shrinks the file, and a tool that only re-saves it does very little. If your PDF is mostly text, expect a modest saving. If it is a scan or full of photos, expect a big one, often more than half.

Check what is inside before you compress anything. A PDF of plain text and vector shapes is usually well under 1 MB, so a 20 MB file almost always means images. Scanned documents are the classic case: every page is a photo of paper, stored at the scanner's resolution. Phone-scanned receipts, exported slide decks with full-size screenshots and Word files with pasted photos behave the same way. Embedded fonts add a few hundred kilobytes at most. Knowing the cause tells you the fix: images get recompressed, while fonts and page structure cannot be shrunk much.

A browser tool is the fastest route for most people. In PixelTools you drop the PDF onto Compress PDF, choose Smallest file, Balanced or Best quality, and download. The file is processed on your own device, so a contract or ID scan never gets uploaded. The default is Balanced. Under the hood each setting is two numbers: a JPEG quality and a maximum image size. Smallest file uses 40% quality and 1200 pixels on the long edge, Balanced uses 60% and 1600, and Best quality uses 75% and 2000. The result screen reports how many images were recompressed, so you can see the effect.

On a Mac, open the PDF in Preview, choose File, then Export, and pick the Reduce File Size Quartz filter. It is quick but blunt: it applies one aggressive setting and often leaves pages visibly soft, so check the result before sending. In Adobe Acrobat, use File, Save as Other, then Reduced Size PDF, or the Optimize PDF panel when you need control over image downsampling. Acrobat has the most settings and a paid subscription. Windows has no built-in equivalent, since Print to PDF re-saves the file without recompressing the images inside it.

Pick by what the PDF will be used for. For email attachments and web forms, use the smallest setting: 1200 pixels on the long edge is plenty for reading on screen, and text in a scan stays legible. For documents people will print, use Balanced or Best quality, because 40% JPEG quality shows blocky edges around small print. Compress once, from the original file. Compressing an already-compressed PDF again stacks lossy passes and degrades the pages further for little extra saving, so keep the original and redo from there if the first result is too soft.

Some files will not get much smaller, and that is normal. A compressor that recompresses JPEG images skips PNG, TIFF and raw bitmap pages, skips CMYK photos it cannot decode safely, and keeps an image's original bytes unless the new version is at least 10% smaller. Text-only PDFs have no photos to work on. If your result is within a few percent of the original, see why a compressed PDF can stay huge for the cause and the workarounds. For a hard email limit, splitting the PDF into two parts is often easier than squeezing harder.