Compressing
How to Compress a Scanned PDF
Scanned PDFs are the easiest kind to shrink — 80% reductions are normal. Here is how to get them without making the text unreadable.
Scanned documents are enormous and they compress beautifully. A 60 MB scan coming out at 4 MB with the text still perfectly crisp is an ordinary result, not a lucky one.
Why the savings are so large
Scanners are set conservatively — 600 DPI, full colour, minimal compression — because they cannot know what the document will be used for. For a page of black text on white paper, almost all of that data is describing nothing. Colour information for a monochrome page, and resolution far beyond what any screen will show, are both pure overhead.
Compress a scan
- 1Run OCR first if you want the document searchable — OCR reads the image better before it is degraded.
- 2Open the Compress PDF tool and add the file.
- 3Choose a moderate setting to start with.
- 4Check the smallest text on the busiest page at 100% zoom.
- 5Step up the compression if you need more and the text is still comfortable.
How far you can push it
| Target resolution | Result |
|---|---|
| 300 DPI | Print quality retained; modest savings |
| 200 DPI | Excellent on screen, fine for most printing |
| 150 DPI | Good on screen; small print starts to soften |
| 100 DPI | Body text readable, fine detail lost |
| 72 DPI | Too far for documents — noticeably degraded |
150–200 DPI is the sweet spot for a document that will be read on screen and occasionally printed. It is where the file becomes manageable and nothing important disappears.
Greyscale and black-and-white
Converting a colour scan of a black-and-white document to greyscale removes roughly two thirds of the data before any other compression is applied. Going further to pure black-and-white is smaller still, but it destroys signatures, stamps and anything faint — worth it for a clean printed form, risky for anything handwritten.
Do it right at the scanner
The best compression is the data you never capture. Setting the scanner to 300 DPI greyscale for ordinary text produces files a fraction of the size with no meaningful loss, and saves you this step entirely.
Do it now
Compress PDF
Reduce file size while maintaining quality. It runs in this browser tab — your file is not uploaded anywhere.
Open Compress PDFFrequently asked questions
How small can a scanned PDF get?+
Reductions of 70–90% are routine. A 60 MB scan at 4–8 MB with readable text is a normal outcome.
Will compression break my OCR text layer?+
No. The text layer is text and survives image compression untouched — which is why OCR should come first.
Should I use black-and-white mode?+
Only for clean printed documents. It destroys signatures, stamps and faint marks.
My scan barely compressed. Why?+
It may already be at a low resolution, or it may have been compressed before. Compressing an already-compressed image costs quality and saves little.