How do I compress a PDF without losing quality?

Use lossless compression, which restructures the PDF's internal data without touching images or fonts — quality is identical, files typically shrink 5–30%. Lossy or 'strong' compression shrinks far more but rasterizes pages, so only use it for scans where selectable text isn't needed.

Why is my PDF so large?

The usual culprit is high-resolution images, especially scanned pages saved at 300+ dpi in colour. Embedded fonts, thumbnails and inefficient internal structure add to it. Image-heavy PDFs benefit most from compression; text-only PDFs are already small.

Does compressing a PDF reduce its quality?

It depends on the mode. Lossless compression keeps quality identical. Lossy compression reduces image resolution to save space, which is fine for screen viewing or scans but visible if you zoom in or print at high quality. Choose based on how the file will be used.

How to Compress a PDF Without Losing Quality

Why PDFs get huge, the difference between lossless and lossy compression, and how to shrink a PDF for email while keeping it sharp — all in your browser.

You finish a document, go to email it, and hit the wall every office worker knows: “file too large.” PDFs have a habit of ballooning to tens of megabytes. The good news is that most of that size is recoverable — often without any visible quality loss at all. Here’s how to do it properly.

Why PDFs get so big

A PDF is a container. Its size is driven mostly by what’s inside:

Images are the main offender. A single full-page colour scan at 300 dpi can be several megabytes. Ten of them and you have a 30 MB file.
Embedded fonts add a few hundred kilobytes each.
Inefficient structure — duplicated objects, uncompressed internal streams, leftover edit history — quietly pads the file.

Knowing this tells you where the savings are: a text-only report is already tiny and barely compresses, while a scanned document is where the big wins live.

Lossless vs. lossy: the key decision

There are two fundamentally different ways to shrink a PDF, and choosing the right one is everything.

Lossless compression — identical quality

Lossless compression rewrites the PDF’s internal structure more efficiently: it compresses the object streams, removes duplication, and tidies the file — without touching your images or fonts at all. The result looks pixel-for-pixel identical to the original.

Quality change: none. Text stays selectable, images keep full resolution.
Typical saving: 5–30%, depending on how wastefully the original was built.
Use it for: anything where quality matters — reports, presentations, documents with selectable text.

This is the answer to “compress without losing quality.” Start here.

Lossy (strong) compression — much smaller, for scans

Lossy compression re-renders each page as an optimized image at a lower resolution. It can shrink a bloated scan by 80% or more — but the page becomes an image, so text is no longer selectable and fine detail softens.

Quality change: visible if you zoom or print at high quality.
Typical saving: very large, especially for scans.
Use it for: scanned documents you’ll read on screen or email, where small size matters more than perfect fidelity.

Rule of thumb: try lossless first. If the file is still too big and it’s a scan, step up to strong compression. For documents with real text you want to keep selectable, stay lossless.

Step by step

Open the Compress PDF tool.
Add your PDF.
Choose a mode:
- Lossless — same quality, modest savings.
- Strong (150 dpi) — big savings, good for most scans.
- Extreme (96 dpi) — smallest size, for screen-only documents.
Compress, check the before/after size shown, and download.

Because it runs in your browser, even a 100 MB+ scan compresses locally with no upload and no file-size limit.

Three more ways to shrink a PDF

Compression isn’t the only lever:

Convert to grayscale. If a document doesn’t need colour — most text scans don’t — converting to black and white shrinks it substantially and is perfect before printing.
Resize the pages. Oversized pages carry more data; normalizing to A4 can help.
Compress before merging. If you’re going to merge several PDFs, compress the heavy ones first so the combined file starts small.

Avoid the double-compression trap

Compressing an already-compressed file rarely helps and can make things worse — re-compressing JPEG images degrades them each time. If lossless compression barely shrinks your file, that’s actually good news: it means the PDF is already efficiently built. Don’t keep re-running strong compression hoping for more; you’ll just lose quality for little gain.

The private way to compress

Most “compress PDF online” services upload your file to a server to do the work — which, for a confidential report or a scanned ID, means sending a full copy to a stranger’s machine. There’s no need: compression is exactly the kind of task a browser can do on its own.

The Compress PDF tool runs entirely on your device. Your file is never uploaded, there are no size limits, and you can see the exact savings before you download. Sharp files, smaller size, and nothing leaves your computer.