Guide4 min readJuly 15, 2025

How to Compress a Scanned PDF (The Right Way)

Scanned PDFs are the biggest offenders — a 10-page scan can be 50MB+. Here's how to shrink them dramatically while keeping text readable.

Why Scanned PDFs Are So Large

When you use a printer's scan-to-PDF function, it takes a photograph of each page at 300 DPI (sometimes even 600 DPI). That means a single page is stored as a 2–5MB image file — even if the page is just black text on white paper.

A 10-page scanned contract? Easily 30–50MB. A scanned book chapter? 100MB+.

How Much Can You Compress a Scanned PDF?

Scanned PDFs respond to compression better than any other type. Here's what to expect:

Scan Quality	Recommended	Extreme
600 DPI scan	85–95% smaller	95%+ smaller
300 DPI scan	70–85% smaller	85–95% smaller
150 DPI scan	40–60% smaller	60–75% smaller

A 50MB scanned contract can realistically become 3–7MB on Recommended, or 1–3MB on Extreme.

Which Level to Choose for Scanned Documents?

Recommended — Best for scanned contracts, legal documents, invoices, bank statements. Text remains clear and readable. Photos on the page look fine on screen.

Extreme — Best for documents that are text-only scans (letters, forms, typed pages). The text stays sharp because it's high-contrast. Use this if you need the absolute smallest file for an email or portal upload.

Low — Best if the scan will be printed again or needs to be archived at the highest possible quality.

Does It Affect OCR (Searchable Text)?

If your PDF already has OCR (searchable/selectable text) applied, compression preserves the OCR text layer. You will still be able to search, copy and paste text from the compressed file.

If the scanned PDF is image-only (no OCR), compression does not add OCR — it remains image-only, just smaller.

Step-by-Step: Compress a Scanned PDF

Go to compress-pdf.site

Choose Recommended (or Extreme for maximum shrinkage)

Drop your scanned PDF into the upload area

Compression starts automatically

Download your compressed file — typically 70–90% smaller

Tips for Getting the Best Results

Always compress the original scan — not a previously compressed copy. Re-compressing an already-compressed file gives diminishing returns.

If the result isn't small enough on Recommended, try Extreme.

If you're scanning specifically to then compress, scanning at 200 DPI instead of 300 DPI produces a much smaller original without any visible quality loss on screen.

Ready to try it?

Free PDF compression. No signup. Files deleted after 1 hour.

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