Other PDF Issues

How to Scan Large Black-and-White Documents into Small PDF Files

Camila Milosovich Oct 22, 2026 868 views

Question details

The user needs to reduce the file size of a large, 70-page black-and-white scanned document so it can be sent via email.

How to Scan Large Black-and-White Documents into Small PDF Files

Product: PDF Scanner Tools
Device & OS: not provided
Scenario: Scanning a multi-page physical document and preparing it for email transmission.
Observed behavior: The resulting scanned PDF file is too large to meet standard email attachment size limits.

Before you start

Before scanning, ensure your scanner software is up to date and check your email provider's maximum attachment size limit (typically 20MB or 25MB).

Solution 1Recommended

Optimize Scanner Settings Before Scanning

Prevent large files from the start by configuring your scanner's resolution and color mode to prioritize text over photos.

Select the correct color mode

Open your scanner software and set the color mode to 'Black and White' or 'Grayscale' rather than 'Color'. Color scans significantly increase file size, even for black-and-white text.

Lower the DPI resolution

Adjust the scanning resolution to approximately 150 to 200 DPI. This is the optimal range for reading text without creating unnecessarily heavy files.

Choose document optimization

If your scanning software has preset profiles, select 'Text', 'Document', or 'Email Optimization' instead of 'Photo' quality.

Disable unnecessary OCR

Only enable Optical Character Recognition (OCR) if you specifically need the text to be searchable. OCR processing adds extra data to the final PDF file.

Optimize Scanner Settings Before Scanning

Test Scan: Always scan just one or two pages first to verify that the text remains legible at your chosen DPI before committing to scanning all 70 pages.

Solution 2

Compress the PDF After Scanning

Use PDF compression tools to reduce the size of an already scanned large document.

Fast & Easy PDF Compression

Compress Large Scanned PDFs Quickly with WPS Office

WPS Office offers a built-in PDF compressor that can instantly shrink large black-and-white scanned documents, making them perfect for email attachments without sacrificing readability.

1. Open the PDF in WPS Office: Launch WPS Office and open your large scanned PDF document.
2. Access the PDF Compressor: Navigate to the 'Tools' tab on the top ribbon and click on the 'Compress' button.
3. Select Compression Level: Choose between 'HD', 'Normal', or 'Common' compression levels based on your required email attachment size limit.
4. Compress and Save: Click 'Compress' to reduce the file size, then save the newly optimized document to your computer.

Easily compress large PDF files with a single click.Fully compatible with standard Adobe PDF formats.Offers multiple compression levels to balance size and quality.Free, lightweight, and user-friendly interface for seamless document management.

microsoft office alternative - wps office

Frequently Asked Questions

What is the best DPI for scanning black-and-white documents?

For standard black-and-white text documents, a resolution of 150 to 200 DPI is generally the best balance between readable text quality and a small file size.

Why is my black-and-white PDF still so large?

It may have been scanned at a very high resolution (such as 600 DPI), saved in a high-quality photo format, or your scanner might still be capturing it in a color mode despite the physical paper being black and white.

Can I compress a PDF on my smartphone?

Yes, you can use mobile scanning apps like WPS Office, which automatically optimize black-and-white documents and offer built-in file size reduction features for easy email sharing.

Does compressing a PDF make it blurry?

If compressed too aggressively, the text can become blurry or pixelated. It is recommended to use 'Document' or 'Standard' compression settings rather than the lowest quality, and always review the file before sending.

PDF Troubleshooting