Open the PDF in a browser-based rotation tool, turn every page or just the selected ones by 90, 180 or 270 degrees, and download the corrected file. The rotation is written into the new PDF itself, so it stays fixed in every viewer, and because the tool runs locally the document is never uploaded.
Hitting the rotate button in a PDF viewer usually only changes how the file is displayed in that session; the next person who opens the document still sees it sideways. Fixing it for good means rewriting the page orientation inside the PDF and saving a new file, which is exactly what a dedicated rotation tool does.
Sideways pages usually come from scanning, where one sheet went through the feeder the wrong way. A tool that can rotate all pages at once, or only the pages you select, lets you fix a single upside-down scan in the middle of an otherwise fine document. Running in the browser, the whole job happens on your device with nothing sent anywhere.
Yes. The orientation is saved into the downloaded PDF, so it opens correctly everywhere.
Yes. You can turn every page or only the pages you select.
No. The rotation happens in your browser and the file never leaves your device.