How to Reduce the Size of a Scanned PDF

Scanned PDFs are often enormous — a single-page scan from a flatbed scanner can be 2–5MB, meaning a 20-page scanned document could be 50MB or more. The good news: scanned PDFs are among the easiest to compress, and the results are dramatic.

Why Scanned PDFs Are So Large

When you scan a document, the scanner captures the page as a high-resolution raster image — essentially a photograph of the paper. This image is stored inside the PDF at full resolution, which might be 300 DPI (dots per inch) or higher.

At 300 DPI, an A4 page image is approximately 2480 × 3508 pixels. An uncompressed image this size is around 25MB. Even with basic JPEG compression applied by the scanner, each page can still be 1–3MB depending on scanner settings and content.

A 20-page scanned contract at those dimensions is easily 40–60MB before any optimization.

How to Compress a Scanned PDF

Scanned PDFs respond extremely well to PDF compression because every page is an image — and image resampling is exactly what PDF compression does. Here's the process:

1. Go to compress-pdf.cc.
2. Upload your scanned PDF (up to 50MB supported).
3. For most scanned documents, select Balanced compression — this will dramatically reduce size while keeping text clearly readable.
4. If you need the absolute smallest file and the content is just typed text on a white background, try Maximum compression — the result will still be readable at normal screen sizes.
5. Download your compressed PDF.

What Size Reduction to Expect

Scanned PDFs typically compress better than any other type. Common results:

• Maximum compression: 70–85% reduction (e.g. 50MB → 8–15MB)
• Balanced compression: 55–75% reduction (e.g. 50MB → 12–22MB)
• Light compression: 30–50% reduction (e.g. 50MB → 25–35MB)

Results vary depending on the original scan quality, resolution, and whether the scanner applied its own compression. High-resolution colour scans compress the most; greyscale scans are usually already more compact.

Preserving Readability

The key concern with compressing scanned PDFs is maintaining readable text. Here's what to watch for:

• Printed text on a clean white background compresses well at all levels — even Maximum usually keeps text perfectly readable.
• Handwritten text and signatures may show more compression artifacts at Maximum level. Balanced is safer.
• Colour scans with photos or charts should use Balanced or Light to preserve visual accuracy.

After compression, always view the result at 100% zoom in your browser or PDF viewer to verify text and signatures are still clearly legible before sending or filing the document.

A Note on OCR (Searchable Text)

Some scanned PDFs have been processed with OCR (optical character recognition) — a layer of invisible searchable text added on top of the images. PDF compression does not remove or affect OCR data. Your compressed scanned PDF will remain searchable if it was searchable before compression.