Straighten a scanned PDF

How it works

1. Drop the scanned PDF. It is read in the browser; the file never leaves your computer.
2. Leave Measure on "Every page on its own" if the pages went through the scanner one at a time. Choose "Use the first page for all" for a stack fed in together, where every sheet is off by the same amount — it is faster, and steadier on pages that are mostly blank.
3. Leave the angle box empty to have the tilt found for you. Type a number only to overrule it: -1.5 turns every page one and a half degrees anticlockwise.
4. Press Straighten PDF. The note under the result says how many pages were turned and how crooked the worst one was.

Frequently asked questions

How does it know which way the page is tilted?

From the rows of ink. Each page is rendered once, and the tool tries every angle up to 10 degrees either way, keeping the one at which the lines of text collapse into the sharpest rows, to a tenth of a degree. If the page has too little ink to read a direction from, or so much that it is a photograph rather than a document, it is left alone rather than turned by a guess.

Does it turn the pages into pictures?

No, and that is the point. Each page is placed into a new one and drawn back at the corrected angle, so a scan keeps exactly the resolution it arrived with, and a PDF that has real text underneath keeps it selectable and searchable. Tools that deskew by rasterising cost you both.

What happens at the corners?

The page keeps its size, so turning it brings in a little white at the corners and pushes a little of the old corners out of view. On a document this is the right trade: the text of a scan sits well inside the margins, and a page that grew to fit its own rotation would no longer be A4 or Letter.

My scan is sideways or upside down.

That is not tilt, and this tool will not touch it — it only turns pages up to 10 degrees, because beyond that a page is the wrong way round rather than crooked. Use Rotate PDF for quarter turns, then come back here if it is still a degree or two off.

What about links, form fields and comments?

They are lost. Turning a page means redrawing its contents, and annotations live outside those contents, so they do not come along. For a scan there is usually nothing to lose; if your PDF is a filled form or has links you care about, straighten it before you add them.

Is it uploaded?

No. The PDF is opened, measured and rebuilt inside the browser tab. Nothing is sent to a server, which is also why a large scan takes a moment on a slow machine.