Quick fix: Open scanner app (NAPS2, HP Smart, etc.) → Scan settings. Set Resolution to lower DPI. Recommendations: 150 DPI for text email, 300 DPI for printable documents, 600 DPI for photos and fine detail. Higher DPI = larger files. Bonus: pick Black & White for text-only scans.

Your scanned PDFs are massive — 5 MB per page or more. Email size limits reject them. Cloud storage fills fast. The cause is too-high scan resolution and/or color when grayscale would suffice. Adjusting both shrinks files dramatically.

Symptom: Scanned documents produce excessively large PDF files; want to reduce size for email/sharing.
Affects: Windows 11 (and Windows 10) with scanners.
Fix time: ~5 minutes.

What causes this

Scan file size scales with: Resolution (DPI): 600 DPI scan is 4× the size of 300 DPI. Color: color is 3× the size of grayscale, which is 8× the size of B&W. Format: PDF with embedded raw images is large; PDF with JPEG compression is smaller. Page count: per-page costs add up.

Method 1: Set appropriate resolution per use case

The primary file-size lever.

Open your scan app (NAPS2 is good free choice). Find scan settings.
Set Resolution / DPI:
- 100–150 DPI: web-only viewing, text emails. ~100 KB per page.
- 200 DPI: balanced text legibility. ~200 KB per page.
- 300 DPI: high-quality text, archival. ~400 KB per page.
- 600 DPI: photos, fine text, small print. ~1.5 MB per page.
- 1200 DPI: ultra-high (photo enlargements, archival fine art). 5+ MB per page.
For text-only documents: 200–300 DPI plenty. 300 DPI for OCR accuracy.
For receipts/contracts (mixed): 300 DPI.
For photos in album: 600 DPI.
For most documents: avoid 600+ DPI unless specifically needed.

This is the main file-size reduction.

Method 2: Use B&W or grayscale for text scans

Color mode multiplies file size.

For pure text (printed, signed papers): pick Black & White (1-bit). Files are 10× smaller than color.
For text with light shading or annotations: Grayscale (8-bit). 3× smaller than color.
For photos and color-printed material: Color (24-bit). Only when color is needed.
In NAPS2 / HP Smart / vendor apps: pick from Color Mode dropdown before scanning.
For mixed pages (some text, some color): use Color for the whole batch — converting later is harder than scanning once correctly.
For PDFs you want to send via email: B&W keeps file under common 10 MB email limits even for long documents.

This is the second major lever.

Method 3: Optimize PDFs post-scan

For files you’ve already scanned at high settings.

Open PDF in Adobe Acrobat Pro (paid) → File → Save As → Reduced Size PDF. Compresses images, removes redundant data. Often 50% smaller.
For free alternative: SmallPDF (online, smallpdf.com) → Compress PDF. Several quality settings.
Or iLovePDF (online) → Compress. Free for occasional use.
For batch compression: PDF24 Creator (free, Windows) has a PDF Compressor tool.
For technical: use Ghostscript:
```
gswin64c -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -sOutputFile=small.pdf large.pdf
```
PDFSETTINGS options: /screen (smallest), /ebook (balanced), /printer (high quality), /prepress (highest).
For NAPS2 specifically: when saving PDF, pick Quality slider — Medium gives good size/quality balance.

This is the right path for compressing existing large PDFs.

How to verify the fix worked

Scan a test document with new settings. Check file size: ideally under 1 MB for a few text pages.
Open the PDF. Text is legible. OCR works if enabled.
If file is too large still: lower DPI further or compress post-scan.

If none of these work

If files are still too large: OCR adds size: searchable PDFs include text layer plus image. The image is what makes it big. OCR text adds <1% to size. Lowering image quality (resolution) is the only way to shrink. For very text-heavy documents: skip image-based PDF entirely. OCR with Microsoft Word or Adobe to convert to editable doc. File size drops 100×. For PDFs that need to retain image quality: use JBIG2 compression (in Acrobat Pro Optimize PDF). Best for B&W document scans. For multi-page TIFF instead of PDF: TIFF with LZW compression can be similar size to JPEG. Convert with IrfanView. Email size limits: 25 MB is common Gmail/Outlook max. Files over 25 MB need to be uploaded to OneDrive/Google Drive and shared via link. Configure auto-upload in email client.

Bottom line: Lower DPI (150–300 for documents) + Black & White for text. Post-scan compression for already-large PDFs. NAPS2 with quality settings is good free workflow.