Auto-detect and straighten crooked scanned pages with live preview and manual fine-tuning
WhiskFile Deskew PDF is a free online tool to auto-detect and straighten crooked scanned pages with live preview and manual fine-tuning. Files are processed entirely in your browser — nothing is uploaded to any server.
Quick Answer
Auto-detect and straighten crooked scanned pages with live preview and manual fine-tuning. WhiskFile's Deskew PDF is free, works in your browser, and requires no account. Your files never leave your device — all processing happens locally.
Upload your scanned PDF
Drag and drop or click to select a PDF with crooked scanned pages. The tool supports multi-page PDFs of any size.
Review auto-detected angles
The tool automatically analyzes each page and detects its skew angle using projection profile analysis. Confidence levels (high/medium/low) indicate detection reliability.
Fine-tune with manual slider
Adjust any page's angle with the -15° to +15° slider (0.1° precision). The live preview updates instantly. Use the before/after toggle to compare.
Configure settings
Choose DPI (150/200/300), background fill color (white/black/custom), and enable auto-crop to trim rotated corners. Toggle the grid overlay to verify alignment.
Deskew and download
Click Deskew & Download to process all pages with their configured angles. Each page is rotated, optionally auto-cropped, and reassembled into a clean PDF.
Verify the result
Open the downloaded PDF and check that text lines are horizontal on every page. Re-process any pages that need further adjustment.
Max file size: 50 MB (free) · 500 MB (paid). Processing time: ~10s on average. Upload one file at a time.
Deskew PDF runs entirely in your browser — no software to install. Works on any device with a modern browser.
Windows & Mac
Chrome, Firefox, Edge, Safari
iPhone & Android
Safari, Chrome mobile
iPad & Tablets
Full touch support
Unlike server-based tools that upload your documents, WhiskFile processes everything locally in your browser. Your files never leave your device — not even temporarily.
No upload required
Files are processed in your browser — nothing is sent to any server
100% private
No server storage, no data collection, no third-party access
Works offline
Once loaded, works without an internet connection
“Compressed PDFs email in seconds instead of minutes. My clients love the fast turnaround.”
Tom Wilson
Real Estate Agent
“OCR on scanned papers makes them searchable instantly. A massive time-saver for literature reviews.”
Emily Zhang
Academic Researcher
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Client-side processing
This tool now runs entirely in your browser — files never leave your device.
Result preview & sharing
Preview your processed file before downloading, and share results via a secure link.
Yes, for scanned image PDFs. Text-native PDFs (created in software) don't have skew issues. The tool works best on text-heavy scanned documents.
The tool detects and corrects skew angles up to ±15°. Each page is analyzed independently. For pages rotated 90° or 180°, use our Rotate PDF tool first.
High confidence means clear text lines were detected and the angle is reliable. Medium means some ambiguity. Low means the page may lack enough text for reliable detection — use the manual slider to fine-tune.
Deskew before running OCR. Straightened pages produce significantly more accurate OCR results.
No. Everything runs entirely in your browser using JavaScript. Your PDF never leaves your device.
When a page is rotated, white triangles appear in the corners. Auto-crop trims these away to give you a clean rectangular page.
The tool uses projection profile analysis — a proven algorithm from document image processing. It scans horizontal text line density at different angles (-15° to +15°), first in 1° steps then in 0.1° refinements, to find the angle that produces the sharpest text rows. This works best on text-heavy pages.
Yes. Every page has a slider from -15° to +15° with 0.1° precision. The auto-detected angle is pre-filled, but you can override it. The live preview updates instantly as you drag the slider.
The grid overlay draws horizontal and vertical reference lines over the preview image so you can visually verify that text lines are truly horizontal after correction. Toggle it on or off with one click.
White is best for most documents (matches the page). Black is useful for documents with dark borders. You can also pick a custom color. Auto-crop removes the fill areas entirely if enabled.
200 DPI (default) is a good balance for most scanned documents. Use 150 DPI for faster processing of large multi-page PDFs. Use 300 DPI for high-quality print output or when you need maximum detail.
Yes. Every page is processed independently. The thumbnail grid shows all pages with their detected angles and confidence levels, so you can quickly identify which pages need manual adjustment.
Yes. Deskew PDF is completely free with no signup, no task limits, and no watermarks. The entire process runs in your browser — your files never leave your device.
Yes. Deskew PDF runs entirely in your browser using WebAssembly. Your files are never uploaded to any server — they stay on your device throughout the entire process. No data is transmitted, stored, or accessible to WhiskFile or any third party.
Yes. Deskew PDF works on any device with a modern browser — iPhone, Android, iPad, tablets, Chromebooks, and desktop computers. No app download required. The interface adapts to your screen size automatically.
Deskew PDF accepts PDF files as input and produces PDF output. The maximum file size is 50 MB on the free plan (500 MB for Pro users). There are no page count limits.
See how WhiskFile compares to other PDF tools on features, pricing, and privacy.
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How to Rotate PDF Pages and Save the Changes
Rotate PDF pages permanently — fix landscape pages, sideways scans, and mixed orientation documents. The rotation is saved in the file, not just your viewer.
Chromebook & Linux
Any modern browser
