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How to Compress a Scanned PDF Without Making the Text Blurry

By the PDF Swing team · Updated 28 September 2026 · 3 min read

Scanned PDFs are big because every page is a picture. The trick to compressing them is to reduce the image data without crossing the point where small print, stamps and signatures turn into mush. This guide explains where that point is, which settings to use, and how to check the result before you submit it.
Key takeaways
  • For scans, the Recommended mode keeps text readable while cutting size several times over.
  • Use the live preview to check the smallest text on the page before downloading.
  • Greyscale is enough for most documents and saves a lot of space.
  • If a strict limit forces too much compression, remove pages or rescan at 150–200 DPI instead.
  • Compression runs in your browser — scanned IDs and certificates are never uploaded.
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Why scanned PDFs are big — and where blur comes from

A scanned page is stored as an image. At 300 DPI in colour, an A4 page is about 2,500 × 3,500 pixels. Compression shrinks it by lowering the resolution, reducing colours, or raising JPEG compression — or all three.

Blur appears when resolution drops below what the smallest text needs. Body text at normal size stays readable down to around 120–150 DPI; tiny footnotes, seal impressions and handwriting need more. JPEG artefacts — the smudgy halos around letters — appear when compression is pushed too far.

The settings that keep text sharp

Open Compress PDF and drop your scan in. For scanned documents the tool typically suggests Recommended, which is the right starting point: it downsamples images to a resolution that still prints and reads well, and uses moderate compression.

Look at the live preview on the right and zoom into the smallest text on the page. If it is clean, download. If the portal allows more size, choose a gentler setting from the Quality tab; if you need smaller, try Target Size with your limit and check the preview again.

When the portal limit is very strict

Some forms ask for 50 or 100 KB for a multi-page document. Compression alone may make that unreadable. Better options, in order: remove pages that are not required with Split PDF; scan in greyscale; crop wide margins so the page is mostly text; and only then compress to the target.

Always check the final file at 100 % zoom before submitting. A file that uploads but cannot be read gets rejected at verification.

Scanning tips that make compression easier

Scan at 200 DPI for normal documents and 300 DPI only when there is very small print. Use greyscale for black-and-white pages. Place the page straight and close the scanner lid fully to avoid grey borders — those borders are pure file size.

With a phone scanner app, choose the “document” or “black & white” filter rather than “photo”. It increases contrast and removes the paper tint, which compresses dramatically better.

Checking the compressed file

After downloading, open the file and zoom in on names, numbers and dates — the details a verifier cares about. Check any photo, signature or stamp. If something is unclear, go back and use a gentler setting; Compress PDF keeps your original untouched, so you can try again as often as you like.

What to do next

Open Compress PDF, pick Recommended and check the live preview before you download.

Remove pages the portal does not need with Split PDF — it is the easiest way to hit a strict limit.

Want the scan searchable too? Run it through OCR PDF after compressing.

Trim wide scanner borders with Crop PDF so each page is mostly text.

Recommended tools

Compress PDF
Compress PDF
Split PDF
Split PDF
OCR PDF
OCR PDF
Crop PDF
Crop PDF

Frequently Asked Questions

What DPI should a scanned PDF be?

200 DPI is a good balance for documents. 150 DPI is fine for plain text read on screens; 300 DPI is only needed for very small print or detailed seals.

Why is my compressed scan blurry?

The compression was too strong for the text size. Use Recommended instead of Extreme, or set a slightly higher target size, and check the preview before downloading.

Does compressing remove the OCR text layer?

Compression works on images and keeps the document structure, so an existing searchable text layer is normally preserved. Run OCR PDF after compressing if you need the text searchable.

Can I compress several scans at once?

Compress them one at a time for the best control, or merge them first with Merge PDF and compress the combined file once.

Is it safe to compress an Aadhaar or marksheet scan here?

Yes. Compress PDF runs in your browser, so the file never leaves your device.

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