How to rotate PDF pages

Most PDF readers have a rotate-view control, and it does what it says: it rotates the view. The bytes on disk are unchanged, so the page is still stored sideways and everyone else still receives it sideways. Some readers remember the setting per document in their own preferences, which is worse, because the page then looks correct to you and wrong to every recipient.

What this tool changes is the page dictionary, where a /Rotate entry records a multiple of 90 degrees that any conforming viewer must apply when displaying that page. Once it is written, the orientation is a property of the document.

The practical test is to open the saved file somewhere you have not touched — a different browser, a phone, a colleague. If it looks right there, the rotation is in the file.

Setting /Rotate does not touch the page content stream. The glyph runs and images keep their original coordinates and their original data; only the instruction about how to present them changes. Nothing is re-rendered and no quality is lost, and the file size changes by a handful of bytes.

That also makes it perfectly reversible. Rotating by 90 and then by 270 returns to the original value with no accumulated degradation, unlike rotating a raster image, where each turn can resample the pixels.

One consequence to expect: because /Rotate is presentation and the MediaBox is unchanged, the page dimensions as stored stay as they were. A rotated A4 page still reports 595 × 842 points while displaying as 842 × 595, which occasionally matters to software reading the geometry directly.

Look at where the top of the text points. If the text reads bottom-to-top — its top edge on the left of the screen — you need 90 degrees clockwise. If it reads top-to-bottom with its top edge on the right, you need 270. If the words are legible but inverted, it is 180.

Scanned batches often need more than one value, because sheets went through the feeder in different orientations. Handle it as two or three runs: list the pages needing 90 and rotate them, then take that output and list the pages needing 270. It is not elegant but it is exact, and per-page rotation is why the pages field exists.

If a page looks tilted a few degrees rather than turned a quarter, rotation is the wrong tool. /Rotate only takes multiples of 90, and a small skew from a crooked scan is a deskew problem, not a rotation one.