Scanned PDFs are large because every page is a full-resolution image of paper. Compressing them re-encodes those page images at a lower resolution, which usually shrinks a scan dramatically while keeping it readable — all in your browser, with nothing uploaded.
Why scans are so big
When you scan or photograph a document, each page is stored as an image, often at high resolution. A handful of pages can easily reach tens of megabytes. That's why scans blow past email and portal limits far more often than digital PDFs do.
Compress the page images down
Compress PDF re-encodes those page images at a sensible resolution. An 80–95% reduction is common on scans, because there's so much redundant image data to squeeze. The text stays readable; the file just stops being enormous.
Choose the right level
For emailing or uploading, screen resolution is plenty. If the scan needs to be printed at full size later, compress less — or keep the original for printing and send a compressed copy for the upload.
Do you actually need it as an image?
If you only need the text from the scan — to copy it, search it, or reuse it — OCR is a much smaller and more useful option. Image to Text recognises the words on the page so you can work with them as real text, which is a fraction of the size of a page image.
Fewer pages, smaller file
Only need some pages? Split PDF extracts them. Combined with compression, that reliably gets a bulky scan under any limit — and because it all runs on your device, a sensitive scan never leaves your browser.
Why scans are so much larger than documents
A scanned page is a photograph, and at 300 dpi a single A4 page is roughly 8.7 million pixels. Twenty pages is a couple of hundred megapixels of image data. A text PDF of the same twenty pages stores characters and positions and might be 200 KB. That difference is why compression transforms a scan and does almost nothing to a document.
Compression or OCR?
Compression keeps the pages as images and lowers their resolution: fast, and the text stays legible down to a point you should check by eye. OCR is the bigger change — it recognises the words, which lets you keep a much smaller file that is also searchable and selectable. If the scan is a document you will refer back to rather than an artefact you must preserve exactly, OCR is usually the better answer.
Whichever you choose, work from the highest-quality scan you have. Compressing an already-compressed scan gives back little size and costs visible quality each time.