Rotate PDF

Nothing is re-encoded

A rotation in a PDF is a number on the page object — 0, 90, 180 or 270. Readers apply it when they draw the page. Setting it does not touch the content stream, the images or the fonts.

So rotating is lossless and immediate regardless of what is on the page. A 40-megapixel scan rotates as fast as a blank page, and neither loses anything.

Ninety degrees only, and that is the format

The specification allows rotation only in right angles, so there is no way to correct a scan that came in five degrees skew by rotating it. Fixing that genuinely requires re-rendering the page, which means rasterising it and losing the text layer.

Any tool offering arbitrary rotation of a PDF page is doing that conversion behind the scenes. It is worth knowing what you are trading before you accept it.

Why a scan comes in sideways

Scanners and phone cameras write orientation as metadata rather than rotating the pixels, because rotating them costs time and quality. The image is stored the way the sensor read it, with a flag saying which way up it should be shown.

When that image is placed into a PDF the flag sometimes travels and sometimes does not, depending on which piece of software did the conversion. The result is a page whose content is the right way up and whose page rotation is not, or the reverse.

Setting the rotation here fixes the second case cleanly. If the pixels themselves are rotated inside an otherwise correct page, no amount of page rotation will help — that needs the image re-placed, which is a different operation entirely.

Answers

Does rotating reduce quality?

No. It sets a value on the page rather than re-drawing anything, so nothing is re-encoded.

Can I rotate by an arbitrary angle?

Not in a PDF. The format allows right angles only. Anything else requires rasterising the page, which loses the text.

Can I rotate just some pages?

Yes. Select the pages you want and rotate; with nothing selected, every page turns.