How to Compress a PDF to Reduce File Size
“This file is too large to attach.” If you’ve ever hit that message trying to email a scanned document or upload a form to a portal, you need to compress your PDF. This guide explains what makes a PDF large, how compression actually works, and how to shrink a PDF for free right in your browser — without uploading it anywhere.
What makes a PDF file large?
Not all PDFs are big for the same reason. A text-only document (a contract you exported from Word) is usually small already. The heavyweights are almost always scanned documents and image-heavy files — every page is a full photograph, often scanned at a high resolution, so a 10-page scan can easily be 20–50 MB. That’s what compression targets.
How PDF compression works
Compressing a PDF mostly means reducing the resolution and quality of the images inside it. A scan at 600 DPI holds far more detail than you need to read it on screen or print it normally; bringing it down and re-encoding the images at a sensible quality can cut the file size by 70–90% while still looking perfectly clear. There’s a natural trade-off: smaller file versus sharper images, which is why a good compressor lets you choose a quality level.
How to compress a PDF, step by step
- Open the Compress PDF tool and add your file.
- Pick a quality level: Strong for the smallest file, Recommended for a good balance, or Light for the best quality.
- Click Compress PDF. You’ll see the original size, the new size, and the percentage saved.
- Download the smaller file.
Because our tool runs in your browser, your document is never uploaded — the compression happens entirely on your own device.
Choosing the right quality level
- Emailing or uploading a scan? Try Strong first — screen-readable quality at the smallest size.
- Need to print it later? Use Recommended or Light to keep more detail.
- Mixed document? Start with Recommended and only go stronger if it’s still too big.
Why didn’t my PDF get smaller?
If you compress a text-based PDF (like one exported from a word processor) and it barely shrinks — or even grows — that’s expected. Those files are already highly efficient because the text is stored as characters, not images. Compression shines on scanned and photo-heavy PDFs. If a text PDF is your problem, the size is usually fonts or embedded images, and keeping the original is often the better choice.
A note on quality
Image-based compression means the text on scanned pages becomes part of an image rather than selectable text. For most sharing and printing that’s fine, but if you specifically need selectable, searchable text, keep a copy of the original or use a tool that preserves the text layer.
Frequently asked questions
Is it free? Yes, with no sign-up and no watermark.
Is my file uploaded? No — compression happens in your browser, so the file never leaves your device.
How small can it get? For scanned documents, 70–90% smaller is common on the Strong setting.
Will it work on mobile? Yes, though very large files are limited by your device’s memory.