Deskew PDF
Upload a scanned PDF and automatically straighten tilted or skewed pages. Uses projection profile analysis to detect the skew angle of each page and rotates it to align content - processes entirely in your browser with no server upload.
Deskew Settings
Auto analyzes each page's pixel projection to find the best correction angle.
Higher quality produces sharper output but takes longer to process.
Color used to fill the corners exposed after rotation.
Processing rasterizes each PDF page at the selected quality and corrects rotation. Output is a new image-based PDF with straightened pages.
Upload a scanned PDF and click Deskew PDF to auto-straighten pages.
Why Use Our Deskew PDF Tool?
Automatic Skew Detection
Detects skew angles using horizontal projection profile analysis on each page independently. The deskew pdf tool finds the rotation that best aligns text lines without any manual measurement.
Per-Page Correction
Each page is analyzed and corrected individually - useful for multi-page scans where different pages have different tilt angles from the scanner bed or sheet feeder.
Manual Override & Quality Control
Switch to manual angle mode for precise control, choose render quality from 96 to 192 DPI, and select background fill color for the exposed corners after rotation.
100% Private Browser Processing
The deskew pdf tool processes every page locally using JavaScript and Canvas API. Your scanned PDF never leaves your device - nothing is uploaded to any server.
Common Use Cases for Deskew PDF
Scanned Document Archives
Straighten large batches of scanned legacy documents so they look professional and read cleanly in any PDF viewer or document management system.
Contract & Legal Scan Cleanup
Fix tilted contract pages and legal filings scanned from physical copies so alignment is consistent for court submission or client review.
Book & Article Digitization
Correct skew in scanned book chapters, academic papers, and journal articles so the content is properly aligned for reading, OCR, and distribution.
Invoice & Receipt Digitization
Deskew scanned invoices and receipts so financial data sits straight on the page - essential for accounting workflows and expense management systems.
Certificate & Form Straightening
Fix scanned certificates, forms, and official documents that were placed at a slight angle on the scanner glass before archiving or sharing.
Pre-OCR Preparation
Straighten scanned pages before running OCR - aligned text lines dramatically improve character recognition accuracy in any OCR engine.
Understanding PDF Deskew
What is PDF Deskew?
PDF deskew is the process of detecting and correcting the small rotational tilt that occurs when a physical document is placed at a slight angle on a scanner bed or sheet feeder. Even a 1-2 degree misalignment makes text look slanted, which reduces readability and degrades OCR accuracy. The deskew pdf tool automatically measures this skew angle for each page and applies a counter-rotation to straighten the content, producing a clean, level document ready for reading, printing, or archiving.
How Our Deskew PDF Tool Works
- Render each page to a canvas - pdfjs-dist renders every PDF page at the selected DPI to an off-screen canvas for pixel-level analysis. No server upload occurs.
- Detect skew angle - the page is downsampled, converted to a binary image, and analyzed using horizontal projection profile analysis. The algorithm searches rotation angles from −10° to +10° and finds the angle that maximises row-sum variance - the signature of well-aligned horizontal text.
- Correct and download - each page canvas is counter-rotated by the detected angle, embedded as a PNG image into a new PDF document, and downloaded instantly. A per-page results summary shows every detected correction angle.
What Gets Corrected
- Scanner bed misalignment - small rotational tilt from physical document placement on flatbed or ADF scanners
- Variable per-page skew - each page is analyzed independently so multi-page documents with inconsistent tilt are all corrected individually
- Corner fills - the white (or custom color) background fills the triangular corners exposed after rotation to keep page margins clean
- Text selectability - not preserved in output; the deskew process rasterizes pages to images. Use the PDF OCR tool after deskewing for searchable text
Privacy, Security & Availability
The deskew pdf tool processes every page 100% client-side using the Canvas API and JavaScript in your browser. Your scanned PDF is never uploaded to any server. The tool is completely free with no account required, no file size restrictions beyond your browser's available memory, and no watermarks added to the output PDF.
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Frequently Asked Questions About Deskew PDF
The deskew pdf tool automatically detects the skew angle of each scanned PDF page and rotates it to straighten the content. This corrects the tilted or misaligned appearance that occurs when paper is placed at a slight angle on a scanner bed.
The tool renders each page to a canvas, converts it to a binary (black/white) image, and uses a horizontal projection profile analysis to find the rotation angle that maximises alignment of text lines. It searches ±10 degrees to cover all realistic scanner skew ranges.
Yes. Switch the Angle Detection setting to "Manual angle" and enter a specific value between -10 and +10 degrees. Positive values rotate clockwise, negative values rotate counter-clockwise. Use this when you know the exact skew or want to apply the same correction to all pages.
The deskew process rasterizes each page at the selected render quality (96-192 DPI) and saves it as an image-based PDF. Text selectability is not preserved in the output. Use the higher 192 DPI setting for best visual quality on text-heavy documents.
No. All deskew processing runs 100% locally in your browser using JavaScript. Your PDF pages are rendered and corrected on your device - nothing is uploaded to any server.
The deskew pdf tool works best on scanned image-based PDFs where pages were captured at a slight angle. It is most effective when the document has clear horizontal text lines for the auto-detection algorithm to analyze.
Yes. The deskew pdf tool is completely free to use with no account, no page limits, and no watermarks added to your output PDF.