How to compress a PDF
- Tap Choose a PDF and pick the document you need to shrink.
- Pick Light, Recommended or Strong, or type the exact size your form allows.
- Tap Compress the PDF and let it work through the pages.
- Read the size it landed on, then save the file.
What compressing a PDF actually does
A PDF is a container. Most of what makes one heavy is photographs — the picture of each page in a scan — and this page finds those, re-encodes them smaller, and writes them back into the same document. The text stays selectable, the vector drawings stay sharp and the links still work, because none of that is touched.
That is also why results vary so wildly. A scan of a ten-page application is ten large photographs and almost nothing else, so it can lose most of its weight. A PDF exported from a word processor is text, fonts and layout instructions, and there is nothing in it for an image compressor to work on. The same button gives you eighty per cent off one file and three per cent off the next, and neither number is a fault.
The line that tells you which kind of file you brought
Every run reports a plain description of your own document before anything else — something like "Scanned document: 12 images, 94% of the file", or "Text document: 380 KB, and no images at all". It is the difference between understanding a disappointing result and assuming the tool is broken.
Where the images are under about a seventh of the file, the page says outright that there is very little here to work on, rather than leaving you to hunt for a setting that would help. And where the best it can manage saves less than three per cent, it hands your original back instead of a fresh file that is no better.