Updated September 2026
Of every document type run through this tool, scanned PDFs see the largest size reductions by a wide margin — commonly 50–90%. That's not a coincidence of the algorithm; it's a direct consequence of how scanned pages are stored in the first place.
A scanner or a phone scanning app typically captures each page as a high-resolution raster image — often 300 DPI or higher, sometimes uncompressed or only lightly compressed by the scanning software's defaults — and embeds that image directly as one full page of the PDF. A single scanned page at high resolution can easily run several megabytes; multiply that across a 20- or 50-page document and the file balloons fast, even though the actual information on each page (text, a signature, a stamp) doesn't need anywhere near that much data to represent clearly.
For an image-heavy PDF like a scan, this tool's second compression pass — re-rendering each page at 150 DPI and re-encoding it as a JPEG at a moderate quality setting — is usually the one that wins, and it wins by a large margin. 150 DPI is well above what's needed for comfortable on-screen reading and standard printing; the visual difference between a 300+ DPI original and a 150 DPI recompression is rarely noticeable unless you zoom in well past 100% or need to reproduce fine printed detail. See the exact thresholds the tool uses on the How Compression Works page.
A common worry with compression is losing selectable, searchable text — but a scanned page never had that in the first place. It was a picture of a page before you ever opened this tool, and it remains a (smaller) picture of the same page afterward. If you need a scanned document to have searchable text, that requires OCR (optical character recognition), which this tool doesn't perform — compressing a scan makes it smaller, not searchable.
150 DPI is a reasonable default for the vast majority of scanned documents — forms, letters, receipts, everyday contracts. Consider keeping (or separately archiving) a higher-resolution original when:
For everything else — the large majority of everyday scanned paperwork — the compressed version is functionally identical for reading, printing, and sharing, at a fraction of the size.
A single large scanned document (a lease, a long contract) compresses in one pass through the tool. If you regularly scan and need to compress many separate documents — a stack of individually-scanned forms, for instance — the paid batch mode handles several files in one go and zips them together; see the batch compression guide.
If you're digitizing a large stack of paper, scanning at your scanner's default or a middling setting (rather than maxing out resolution "just in case") and compressing afterward gets you nearly the same result as fussing over scanner settings ahead of time — and it's easier to compress an over-scanned file down than to fix an under-scanned one by scanning it again.
It's tempting to try to get the file size right at scan time by lowering the scanner's resolution setting — but most consumer and phone scanning apps don't expose a resolution low enough to matter, and going too low risks a genuinely blurry scan you can't fix afterward. It's generally safer to scan at whatever the app defaults to and let compression handle the size afterward — you can always compress down from a high-quality scan, but you can't add back detail to an under-scanned one.
Will compressing a scan make handwriting or signatures harder to read? At 150 DPI, ordinary handwriting and signatures remain clearly legible on screen and in print — the reduction mainly removes resolution and detail beyond what's needed to read them, not the content itself.
Can I compress a scan and still search its text? Only if the PDF had a text layer from OCR before you compressed it — the compression itself doesn't add or remove a text layer, only image resolution.
Is a compressed scan still acceptable for official submission (tax, legal, government forms)? In most cases yes, since the content and legibility are unchanged — but if a specific institution has its own resolution or file-format requirement, check that requirement directly rather than assuming.