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Deskew scanned pages

Straighten crooked scanned pages automatically or set the angle manually. The output is a raster PDF, nothing is uploaded.

How Deskew scanned pages works

PDF Deskew detects the angle at which each scanned page was fed into the scanner slightly crooked and rotates it back to straight. The detection works by analysing the distribution of dark pixel runs across the rasterised page at multiple candidate angles; the angle that produces the most consistent horizontal alignment is selected and applied. The entire analysis and rotation runs in your browser, and the PDF never leaves your device.

Deskewing is a heuristic process. It works well on pages with clear horizontal text or line structures, which provide a strong signal for angle detection. Pages with mostly vertical content, large images without text, or very light scans may not yield a reliable angle estimate. The tool reports the detected angle per page so you can verify its judgement. If the automatic result is wrong for a specific page, the manual rotation tool can be used to correct that page independently.

Written by Bastien Sulyan

How to use Deskew scanned pages, step by step

  1. Drop your scanned PDF onto the upload area.
  2. The tool analyses each page and displays the detected skew angle.
  3. Review the angle estimates; deselect any page where the detection looks incorrect.
  4. Click deskew and download the corrected PDF.

Common use cases

  • A stack of signed contracts was scanned in a hurry and every page is tilted 1-3 degrees; correct them all before filing.
  • An archive of old letters scanned from physical folders has inconsistent page angles; straighten them for OCR accuracy.
  • A batch of forms scanned on an automatic feeder came out with slight rotation differences; deskew to align them before PDF conversion.
  • A scanned book has pages photographed at mild angles because the book was not fully flat on the scanner glass; straighten them for a clean digital copy.

Frequently asked questions

How accurate is the skew angle detection?

Accuracy depends on page content. Pages with clear horizontal text lines or ruled lines produce reliable detections, typically accurate to within half a degree. Pages with large blocks of images, vertical-only text, or very sparse content may produce less accurate estimates. The tool shows you the detected angle before applying it.

What happens if the tool gets the angle wrong for a page?

You can deselect individual pages before applying the deskew, or skip the whole tool for that page and correct it manually using the PDF Rotate tool set to a precise angle. The detected angle is shown per page so you can make an informed decision.

Does deskewing preserve the text layer if the scan had one?

Deskewing re-renders each page as a raster image and applies the rotation at the pixel level. A text layer embedded in the original (from a previous OCR pass) is not rotated independently and may no longer align with the visual content after deskewing. Running OCR again after deskewing produces a correctly aligned text layer.

Does the scanned PDF get uploaded to a server for analysis?

No. The pixel-level angle analysis and the page rotation both happen inside your browser. Scanned pages can contain sensitive documents; the fact that all processing stays local is especially relevant for this kind of content.

Can I deskew a PDF that was created digitally, not scanned?

Deskewing is designed for scanned pages where the physical paper was fed at an angle. A native digital PDF does not have page skew in that sense; its pages are already rendered at 0 degrees. Applying deskew to a native PDF would likely detect a near-zero angle and produce no meaningful change.