How to Compress a PDF Without Losing Quality
"Compress" makes it sound like one setting, but there's a real tradeoff between file size and image quality — and picking the wrong level either barely shrinks the file or makes your images mushy. Here's what's actually happening, and how to pick correctly the first time.
What compression actually does
A PDF's size mostly comes from two things: its internal structure (fonts, metadata, redundant objects) and its embedded images. Every compression level in Compress PDF cleans up the structural overhead first — that part is always safe and never affects how the document looks. The visible difference between levels comes from how aggressively embedded images get re-encoded:
| Level | Image quality | Max image dimension |
|---|---|---|
| Low | 85% (structure only, images untouched) | Original size |
| Medium | 75% | 2000px |
| High | 55% | 1500px |
| Maximum | 35% | 1000px |
How to pick the right level
- Start with Medium. It's the right default for reports, scanned documents, and anything with photos — a real size reduction with no visible quality loss on a screen or printed page.
- Use Low if the file is already small and you just want to strip unnecessary structural bloat without touching images at all.
- Use High or Maximum only when you're up against a hard size limit — an email attachment cap, a form upload limit — and file size matters more than image sharpness. Maximum is the most aggressive; check the result before sending anything important.
If compression barely shrinks your file
That's expected for text-only PDFs — contracts, plain reports, anything without large images — since there's very little for a compressor to work with. Compression makes the biggest difference on scanned pages and image-heavy documents, where large embedded photos dominate the file size.
Frequently asked questions
Which compression level should I use?
Medium is the right default for most documents — it noticeably shrinks the file while keeping images sharp enough for on-screen reading and normal printing. Reach for High or Maximum only when file size matters more than image fidelity, like email attachment limits.
Why didn't my file get much smaller?
Text-only PDFs are already compact — there's not much a compressor can do to plain text. Compression makes the biggest difference on PDFs with large embedded images, like scanned documents or photo-heavy reports.
Will compression make my PDF blurry?
Only at the more aggressive levels. Low compression only optimizes the file's internal structure and doesn't touch image quality at all. Medium and above re-encode embedded images at a lower JPEG quality and resolution — visible if you zoom in far enough at Maximum, but not at Low or Medium for typical viewing.
Related tools
Combining files before you compress? Use Merge PDF first, then compress the result. Archiving the compressed file long-term? Consider PDF/A Converter afterward for a format built to stay readable for decades.