Compress Scanned PDF Documents 2026 — Free Online

Scans are the case compression was built for. A scanned page is already an image, so rendering it at a lower resolution loses nothing structural — measured here, a 7.21 MB scan came back at 268 KB, a 96% reduction.

Why scans compress so well

A scanner captures the page as a photograph, typically at 300 DPI for archival work or 600 for detail. That resolution is far beyond what anyone needs to read the document on screen, and it is where the size comes from — a 300 DPI colour page is around 25 megapixels of data.

Because the page is already an image, re-rendering it at 144 or 72 DPI costs nothing that a text document would lose. There is no text layer to destroy and no vector artwork to flatten. It is simply a smaller photograph of the same page.

This is why the same tool that shrinks a scan by 96% leaves a text PDF alone: they are entirely different kinds of file that happen to share an extension.

  • Scanners default to 300 DPI; screens need far less
  • 150–200 DPI stays comfortably readable for text
  • 72 DPI is legible but visibly soft on small print

What you lose, and when it matters

If your scanner ran OCR, the file carries an invisible text layer that makes it searchable and selectable. Rendering the pages to images discards it. The document will look the same and no longer be searchable.

For a scan you are sending once, that is rarely a loss worth caring about. For anything going into an archive, a case file or a document management system, it matters a great deal, and the right order is to compress first and run OCR afterwards rather than the other way round.

Colour is the other lever, and it sits with your scanner rather than with this tool. A greyscale scan of a black-and-white document is a fraction of the size of a colour one before any compression is applied.

Choosing a level for a scan

Recommended at 144 DPI is the right default for a scanned text document: comfortably readable on screen, and typically a reduction of 90% or more from a 300 DPI original.

Go to Extreme when a strict upload limit demands it and the document is printed text, which survives 72 DPI. Stay on Low when the scan contains handwriting, signatures, small print or anything someone may need to examine closely — those are exactly the details that soften first.

Frequently Asked Questions

How much smaller will a scanned PDF get?

Usually 90% or more from a 300 DPI original. Measured here: a 7.21 MB scan came back at 268 KB on the default setting, a 96% reduction.

Will compressing a scan make it unreadable?

At 144 DPI, no — it stays comfortably readable on screen. At 72 DPI printed text survives but handwriting, signatures and small print soften noticeably.

Does it remove the searchable text from my scan?

Yes, if the scanner added an OCR layer. Pages are rendered to images and that layer is discarded. If you need the document searchable, compress first and run OCR afterwards.

Why does my scan compress so much better than a text PDF?

A scan is already a photograph of the page, so lowering the resolution costs nothing structural. A text PDF is a short list of drawing instructions, and turning it into photographs makes it larger — which is why the tool leaves it alone.

Should I scan at a lower resolution instead?

For documents you only need to read, yes — scanning in greyscale at 200 DPI produces a file a fraction of the size before any compression. Keep 300 DPI and colour for anything being archived.

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