Scanned PDF too large: what to do
A 10-page scan should weigh 5-8 MB maximum. If yours hits 50+ MB, your scanner is almost always set to 300 DPI color by default when it should be 200 DPI grayscale for most uses. Either you re-scan with the right settings, or you compress the existing PDF. Both solutions are detailed below, with expected reduction ratios.
Decision tree
- →Do you have the original paper document? Re-scan it (Step 2 below). Always better than compressing.
- →Only the PDF, no original? Compress the PDF (Step 3). You lose some quality but it\'s usually invisible on screen.
- →PDF for legal use or pro print? Light compression only (method in Step 5). Don\'t try to reduce too aggressively.
Tutorial: 5 steps to fix the issue
Identify the source of bloat
Open the PDF and check: does it have an OCR layer (selectable text)? Is it color or black and white? How many pages?
Re-scan with the right settings (if possible)
Reconfigure your scanner to 200 DPI grayscale (instead of 300 DPI color default). Typical gain ×3 to ×5 with no readability loss on text.
If re-scanning isn't possible, compress
Use a tool that downsamples embedded images to 150 DPI and re-compresses to JPEG q75. Reduction ratio: ×5 to ×10 for standard scans.
Verify the result at 200% zoom
Text must remain sharp. If you see blur or artifacts in letters, your compression level is too aggressive. Step back to medium compression.
For legal or official documents
Keep 200 DPI minimum and preserve color if document has stamps or signatures whose color matters for evidentiary value. Compression then yields less (×2 to ×3 typical).
Which scanner setting for which use
| Use | DPI |
|---|---|
| Quick email / screen | 150 |
| Internal archive | 200 |
| Document with stamp | 200 |
| Inkjet printing | 300 |
| Pro print / evidentiary | 300 |
| Photo or architectural plan | 600 |
Quick solution
Compress your scanned PDF now
Typical ×5 to ×10 reduction for scans, no text readability loss. Local, free, no signup.
Launch →Frequently asked questions
Why does my scanner produce a 80 MB PDF for 10 pages?+
Your scanner is probably set to 300 DPI color by default. At this resolution, each A4 page weighs 3-8 MB in JPEG. 10 pages × 6 MB = 60-80 MB. Reconfigure to 200 DPI grayscale to drop to 500 KB-1 MB per page.
What scanner setting for what use case?+
Screen reading / email: 150 DPI grayscale (200-400 KB per A4 page). Internal archiving: 200 DPI grayscale (500-800 KB per page). Inkjet printing: 300 DPI grayscale (1-2 MB per page). Document with stamps or essential color photo: 300 DPI color (3-6 MB per page).
Does compressing a scanned PDF degrade OCR (text search)?+
If you compress AFTER OCR, the text layer stays intact (it's not an image). If you compress BEFORE OCR then run OCR, the recognition quality drops because the source image is degraded. Right order: scan → OCR → compress.
My scans are 1-bit black and white, why are they still heavy?+
1-bit (pure black/white) shouldn't exceed 50-100 KB per A4 page at 300 DPI. If your 1-bit scans are heavy, it's probably (a) they're actually grayscale masked as 1-bit, or (b) the OCR layer adds 200-500 KB per page. Check both.
JBIG2 vs JPEG2000 for compressing scans, which to choose?+
JBIG2: very efficient for black/white scans (text), ratio 5-10× better than JPEG. But may substitute similar characters (a 6 read as 8) — risky for legal documents. JPEG2000: ~20% better than classic JPEG for color, but compatibility issues on older PDF readers. JPEG remains safest universally.
My scan has an OCR layer but text is badly recognized, how to redo OCR?+
Adobe Acrobat Pro: Tools → Recognize Text → In This File. Configure language (e.g., English). For free: Tesseract command-line with -l eng. Tesseract reaches 95-99% accuracy on clean 300 DPI scans.
How many KB per A4 page is "normal" for a scan?+
Optimal scan for screen: 150-400 KB/page (150 DPI grayscale). Optimal for archiving: 500-800 KB/page (200 DPI grayscale). High-quality scan: 2-4 MB/page (300 DPI color). Beyond: your scanner is over-sampling or you enabled "auto enhance".