You attach a PDF, hit send, and get the dreaded "file too large" message. Email providers usually cap attachments at around 20–25 MB, and many job portals or government upload forms are far stricter — sometimes just 2 MB. The good news: most oversized PDFs can be shrunk dramatically without you noticing any difference. Here's how PDF size works and how to fix it.
Why PDF files get so large
A PDF that is mostly text is almost always small — a 50-page text document might be under 1 MB. The size problems start with images. A single high-resolution photo or a scanned page can be several megabytes on its own, and a scanner often saves every page as a full-colour 300 DPI image. Ten scanned pages can easily produce a 30 MB file. Embedded fonts, form fields, and saved revision history add a little more on top.
Two kinds of compression
It helps to know that "compressing a PDF" can mean two different things:
- Lossless / structural optimisation — removes hidden metadata, unused objects, and repackages the file more efficiently. Nothing visible changes, but the savings on an image-heavy file are usually small.
- Image downsampling (lossy) — lowers the resolution and re-encodes the pictures inside the PDF. This is where the big reductions come from. A scan saved at 300 DPI looks identical on screen at 110–150 DPI but can be a fraction of the size.
A good compressor tries both and keeps whichever result is smaller — so a text-only PDF that is already tiny is never made larger.
Step by step: compress a PDF
- Open the Compress PDF tool.
- Drag your file in, or click to browse and select it.
- Pick a level: Low keeps the highest quality, Medium is a good balance, and High produces the smallest file.
- Click Compress, then Download the result. The tool shows you the before-and-after size so you know exactly what you saved.
Choosing the right level
If the document will be printed, stay on Low or Medium so text and lines stay crisp. If it's only going to be read on a screen or uploaded to a form, High is almost always fine and gives the smallest file. When in doubt, try Medium first and only drop to High if you still need to get under a limit.
Other ways to shrink a PDF
Compression isn't the only lever. If you only need part of a document, use Split PDF to extract just the pages you want — a 3-page extract is far smaller than the whole 200-page file. And if you accidentally have several PDFs you're emailing one by one, merging them into one tidy file is often easier on the recipient even if it doesn't save space.
A note on privacy
Sensitive documents — contracts, bank statements, passports — should never be uploaded to an unknown server just to be shrunk. Every tool on this site processes your file entirely inside your browser, so the document never leaves your device. You can read more in our guide to online PDF tool safety.