MammothPDF
Tools

Auto-rotate PDF

Pages scanned on their side or upside down are read for the way their text runs and turned upright, each by its own quarter turn, with the result shown before you save. A page with a text layer is read exactly; a plain scan is judged by the shape of its lines. The turn is stored as the page's rotation, so nothing in the file is redrawn.

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Frequently asked questions

How does it know which way a page lies?

Two ways. A PDF with a text layer - anything made from a document, or a scan that went through OCR - says which way its text runs, and that is read exactly. A plain scan is rendered small and its ink measured: level lines of text pile into rows, and Latin text is heavier above the line than below it (capitals, ascenders and accents against a few descenders), which tells up from down. Pages with only a heading or a table of numbers get a ? for you to check.

Does it change the quality of the scan?

No. The turn is written as the page's rotation attribute, the same thing the Rotate tool sets, so no pixel is touched and nothing is re-rendered. Bookmarks, links and form fields stay.

Can I correct a page it got wrong?

Yes. Every page is shown as it will come out; pick the pages and turn them 90° left, 90° right or 180° in the options, or go back to the detected turns.

Is the PDF uploaded?

Nothing is uploaded: the file is opened and processed inside your browser and never leaves your device. Close the tab and it is gone.

Missing something, or did the result surprise you?

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