Rotate PDF turns pages a quarter turn clockwise, a quarter turn anticlockwise, or upside down, and saves the rotation into the file so it opens the right way up everywhere. Rotate every page at once, or switch to Selected pages and pick them by tapping the previews, typing ranges (2, 4-6), or using the odd and even buttons. The previews turn as you change the settings, so you see the result before you save.
The rotation is written with pdf-lib in your browser by changing each page's rotation setting, the same way desktop PDF editors do it. Nothing is redrawn, so text stays selectable, links and form fields keep working, and the file size barely changes. A page that was already rotated in the original is turned further from where it was.
Honest limits: pages turn in steps of 90°, which fixes sideways and upside-down pages but not a scan that is a few degrees crooked. Some viewers remember their own view rotation, which is separate from the file; this tool changes the file itself. Password-protected PDFs need to be unlocked first, and files up to 200 MB are accepted.