Complete guide: Reduce scanned PDF size

Why scanned PDFs are huge

Scanners save each page as a large image. A 300–600 DPI scan can be several megabytes per page, so long documents quickly reach 50–200 MB. Unlike text‑based PDFs, scanned files don’t compress well with simple metadata cleanup.

The good news: scanned PDFs have significant redundancy. Image recompression, careful quality settings, and avoiding unnecessary color data can reduce size dramatically without making text unreadable.

PDFThin focuses on the content that matters: text clarity and page order. You choose the target, and the tool balances size vs readability.

Use Smart quality for scan‑heavy documents

Smart quality automatically searches for the highest acceptable quality that still fits your target size. This is ideal for receipts, IDs, contracts, and reports where small text must remain legible.

If you use a strict size limit (like 20 MB for Outlook), Smart quality will step down the image quality only as much as needed. The result is a smaller file with the best possible clarity for that target.

When scans are very noisy or high‑contrast, a slightly lower target size often yields better results than a maximum‑quality preset.

Choose the right target size

Start with an email preset if you plan to send the file as an attachment. Gmail uses 25 MB, Outlook often uses 20 MB, and Outlook.com supports 25 MB. If your PDF is just above the limit, set a custom target 2–5 MB lower to avoid encoding overhead.

If your document is for storage or upload, choose a practical target that keeps pages readable (often 150–250 KB per page for grayscale scans). For 200 pages, a 30–50 MB target is usually a good starting point.

PDFThin will try to keep page dimensions the same and avoid destructive operations. If a file still cannot fit, use split by size for a guaranteed result.

Practical checklist for scanned PDFs

1) Use Smart quality. 2) Pick an MB target aligned with your delivery channel. 3) If the file is still too large, split into parts. 4) Always preview a few pages to confirm readability.

If you’re scanning in color but only need black‑and‑white output, consider rescanning in grayscale to reduce size at the source. For already‑scanned files, Smart quality offers the most reliable balance.

Start here: Email‑ready compression or Split by size.

Will compression make text blurry?

Smart quality chooses the highest quality that still meets the target size, prioritizing readability.

What target size should I use?

For email, use a preset. For archives, aim for a size that keeps pages readable (often 150–250 KB per page).

What if the file still won’t fit?

Split the PDF into ordered parts under your limit with Split by size.

Related guides

Also see Compress PDF for email and Split PDF by size.

All PDF tools

Browse every PDFThin tool in one place.

Email-ready compression

Shrink PDFs to Gmail/Outlook limits with quality control.

Split by size

Split large PDFs into size-safe parts.

Organize PDF

Merge, rotate, delete, reorder, and split pages.

All PDF guides

Browse every step-by-step PDF guide.

Compress PDF for email (complete)

Step-by-step workflow for Gmail 25MB and Outlook 20MB limits.

Reduce scanned PDF size

Keep text readable while shrinking scanned documents.

Split PDF by size

Create parts that stay under a target MB limit.

Rotate PDF pages online

Fix page orientation for sideways scans or photos.