Question 1

Can I rotate only some pages?

Accepted Answer

Yes. Put the page numbers in the range box — 2, 5-7 rotates just those. Leave it empty to rotate every page, which is what you usually want after a scan came out sideways.

Question 2

Does the rotation stick when I open the file elsewhere?

Accepted Answer

Yes. The rotation is written into each page's own /Rotate entry, which is part of the PDF format, so every reader honours it. It is not a temporary view setting.

Question 3

Why is the file size unchanged?

Accepted Answer

Because nothing is re-encoded. Rotating only changes a number in each page's metadata; the page content is untouched, which is also why it is instant even on a large document.