Compress a Scanned PDF

Compress a Scanned PDF

Scanned documents are exactly what this tool is best at. Every page is an image, usually at a resolution far beyond what anyone needs — so recompressing those images typically removes 70–90% of the file with the pages still perfectly readable. Runs in your browser, nothing uploaded, free.

Why Scanners Produce Such Big Files

Scanner defaults were designed for reproducing photographs, not for emailing a form. Left alone, most machines capture at 300–600 DPI in 24-bit colour, which for a page of black text is enormous overkill.

Notice that readability does not change until the very bottom of that table. Everything above 200 DPI is buying detail that a typed page simply does not contain.

Phone Photos Are Worse Than Scans

Photographing a document with a phone produces the largest files of all: a 12-megapixel camera image, complete with the desk around the page, uneven lighting and perspective distortion. If you have the choice, use a document scanner app rather than the camera — it crops to the page edges, flattens the perspective and compresses sensibly, often producing a file ten times smaller before you compress anything.

A Note on Searchable Scans

Most scans contain no text layer — they are pictures of words, which is why you cannot select anything in them. Some scanners and apps add an invisible OCR text layer on top. If yours did, Smart mode leaves that layer completely intact, so your compressed scan stays searchable. This tool does not add OCR itself; if you need it, run an OCR tool first and compress afterwards.

Frequently Asked Questions

How do I compress a scanned PDF?

Drop it in and press Compress. Scanned PDFs are the ideal case for this tool - every page is an image, so recompressing those images shrinks the file dramatically. Switching on grayscale usually saves another 20-40%.

Why are scanned PDFs so large?

Because scanners default to settings far beyond what a text page needs. A page scanned at 600 DPI in full colour holds roughly sixteen times the data of the same page at 150 DPI in grayscale - and looks no more readable.

Should I use grayscale on a scan?

For typed or printed text, almost always. The colour channels are recording paper tint and scanner noise, not information. For documents with coloured stamps, signatures in blue ink, highlighted passages or photographs, keep colour.

Will the text still be searchable after compressing?

Only if it was searchable before. Most scans contain no text layer at all - they are pictures of text - so there is nothing to preserve or lose. If your scanner added OCR text, Smart mode leaves that layer completely untouched.

Does this add OCR to my scan?

No. This tool compresses; it does not perform optical character recognition. If you need a searchable scan you would need an OCR tool first, then compress the result here.

What resolution should I scan at in future?

200 to 300 DPI in grayscale for text documents. That is fully legible, prints cleanly and produces files that rarely need compressing at all. 600 DPI is for archival reproduction of photographs and fine detail.

Is my scanned document uploaded anywhere?

No - and for scans this matters more than usual, since they are typically passports, certificates, bank statements and signed contracts. Everything is processed on your device.

How much smaller will my scan get?

Typically 70-90%. In testing, a scanned-style document went from 1.1 MB to 263 KB at good quality and 123 KB at stronger settings.