OneClickPDF

How to Deskew a PDF (Straighten Skewed Scans)

Last updated: February 24, 2026

Scanned documents often come out slightly tilted — the paper was fed at an angle, the scanner lid wasn't flush, or the original was placed crooked. Even a 1-2° skew makes text look unprofessional and can cause OCR accuracy to drop. OneClickPDF's deskew tool auto-detects the skew angle on every page and corrects it — entirely in your browser.

Step-by-Step Guide

1

Open the Deskew PDF tool

Navigate to the Deskew PDF page on OneClickPDF. No account or installation required.

2

Upload your skewed PDF

Drag and drop your scanned PDF onto the upload zone. The file stays on your device — nothing is uploaded to any server.

3

Auto-detect skew angles

The tool analyzes every page using a projection profile algorithm and detects the tilt angle automatically. Each page gets its own angle reading with a confidence score.

4

Review and fine-tune

A visual grid shows every page with its detected angle. Thumbnails rotate in real-time to preview the correction. Adjust any page's angle manually with ±0.1° and ±1° controls if the auto-detection needs tweaking.

5

Apply and download

Click Apply Deskew. Pages with corrections are rasterized at high resolution with the tilt removed. Pages with 0° skew are copied losslessly. Download your straightened PDF.

Deskew PDF

Automatically straighten tilted or skewed scanned pages.

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Frequently Asked Questions

How does the auto-detection work?
The tool uses a projection profile method — it renders each page, converts to grayscale, binarizes with Otsu's threshold, then tests rotation angles from -10° to +10° to find the angle that maximizes horizontal line alignment. A two-pass approach (coarse then fine) gives 0.1° precision.
Can I skip pages that don't need correction?
Yes. Enable the 'Skip pages with ~0° angle' option and pages detected at 0° are copied losslessly from the original — no quality loss at all.
Does deskewing affect text quality?
Corrected pages are rasterized at 2x resolution, which looks excellent for viewing and printing. Pages that don't need correction are copied losslessly, preserving selectable text.
Can I deskew a password-protected PDF?
Yes. If your PDF requires a password, you'll be prompted to enter it. The deskew then proceeds normally on your device.
What's the maximum skew angle it can detect?
The tool detects angles from -10° to +10°. Most scanned documents have skew under 5°, which is well within this range.

Skewed scans look unprofessional and hurt OCR accuracy. OneClickPDF fixes both problems with automatic detection and per-page fine-tuning — all in your browser with no upload required.

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