How to compress a PDF without losing quality

"The file is too large to attach." A PDF that won't fit under an email or upload limit is one of the most common document headaches — and almost always fixable. Here's why PDFs balloon, the two real ways to shrink them, and how to do it for free without handing your file to a stranger's server.

Why PDFs get so big

Text is tiny; images are not. A PDF made of typed text and vector graphics is usually small. The ones that get huge are almost always:

Scanned documents — every page is a full-resolution photo.
Image-heavy reports — screenshots, photos, and charts at print resolution.
Files exported at maximum quality — design tools often embed images far larger than the screen needs.

Knowing this tells you where the savings are: the images.

Lossless vs lossy — the honest difference

There are two fundamentally different ways to make a PDF smaller, and it's worth knowing which you're getting.

Lossless (re-save): the file is rebuilt and tidied up — duplicate data removed, structure streamlined — with no change to how it looks. Savings are modest but the text stays perfectly sharp and selectable. Always try this first.
Lossy (downscale images): the embedded images are reduced in resolution. This can shrink a file dramatically, but it rasterises the pages, which means the text becomes part of the image and is no longer selectable. Great for scans you just need to email; not ideal if people must copy text from the document.

Compress a PDF in your browser

The Compress PDF tool does both, locally — your file never leaves your device.

Open Compress PDF and add your file.
Start with the default lossless re-save and check the new size.
If you need it smaller, switch on the downscale images (lossy) mode.
Compare the before/after sizes shown and download the result.

Because it processes everything in the browser, there's no upload, no sign-up, and no watermark.

Tips to keep quality high

Try lossless first. If it gets you under the limit, you've lost nothing.
Only go lossy when you must — and keep the original, since downscaling can't be undone.
Drop pages you don't need. Fewer pages means a smaller file — reorder or delete pages before compressing.
Don't compress twice. Re-compressing an already-lossy PDF mostly just degrades it further for little gain.
For pure scans, a moderate downscale is usually invisible at reading size while cutting the file by half or more.

Other ways (and their catches)

macOS Preview can shrink a PDF with its "Reduce File Size" Quartz filter, but it's Mac-only and often over-compresses. "Print to PDF" can flatten a file but gives you little control over the result. A dedicated tool that shows you the before/after size — and lets you choose lossless or lossy — gives you a predictable result every time.

Shrink your PDF now

The free Compress PDF tool makes a too-big file emailable in seconds, entirely in your browser. While you're there, the other free PDF tools can merge, split, or reorganise your document too.