How to straighten a crooked scanned PDF (deskew)
Updated
Contents
To straighten a scanned PDF whose pages went through the scanner at a slight angle, open OCR PDF, add the PDF, tick “Straighten crooked pages” and press Recognize text. Each crooked page is turned level before its words are read, so the file you download is straight and searchable at once.
The work happens on our secure server, not in your browser. The PDF, up to 100 MB, uploads over an encrypted connection and is deleted when the job ends, and the download link stops working after 60 minutes.
Step by step
- 1Open the OCR PDF tool and drop your PDF on the box that says “Add a scan to OCR, or”, or click browse to pick it.
- 2Under Languages, select the language your pages are written in, and keep Searchable PDF under Output.
- 3Tick “Straighten crooked pages”, and leave “Redo existing OCR” off: the two cannot be used together.
- 4Press Recognize text. The file uploads when you press it, and the button shows the job's progress.
- 5When the job finishes, press the download button that appears, which is named after the file: scan.pdf comes back as scan-ocr.pdf.
Which pages it straightens
Straightening works on scanned pages that have no text yet, which is what a scanner or a phone app usually produces. A page that already has text, typed or recognised before, is kept exactly as it is, so it is not straightened. That is why it cannot be combined with “Redo existing OCR”, which would recognise those pages again.
It takes a PDF. A JPG or PNG added to the same tool is read as it is, without straightening, and the tickbox turns itself off for one. Each page it straightens is saved as a new, level image of that page rather than the original picture, so the downloaded file can be larger than the scan you started with.
Sideways or upside-down pages
Straightening is for a slight tilt, the few degrees a page picks up in a feeder or on the glass. A page scanned sideways or upside down needs “Turn pages upright”, the box beside it: tick both, and in one run each such page is turned the right way up and levelled. A page with only a line or two of text may not be turned; Rotate PDF turns any page you choose by hand.
Common questions
Does straightening change how my pages look?
Only the crooked ones. A page it straightens is saved as a new, level image of that page; the rest keep their original pictures, with an invisible text layer added underneath so the words can be searched and copied.
Why was a page not straightened?
Usually because it already had text, which keeps a page exactly as it was. A page that is sideways or upside down needs “Turn pages upright” ticked as well. And a JPG or PNG is never straightened: only PDFs are.
Can I straighten a scan without making it searchable?
Not on its own. Straightening is part of the recognition run, so the PDF you get back is level and searchable together; the text layer is invisible and does not change how the pages look.
What happens to my file?
It uploads over an encrypted connection to our secure server and is deleted when the job ends, whether it succeeds or not. The download link stops working after 60 minutes, and a daily storage rule erases the stored copy after that.