Short answer
Rotating the view in a PDF reader doesn't stick — reopen the file and it's sideways again. To rotate permanently, use this tool: choose your PDF, pick a rotation, and download. The rotation is written into the file, and it all happens in your browser.
Many readers (including browsers and some viewers) only rotate the on-screen view, not the saved document. This tool changes the page's stored rotation, so the fix is permanent across every device and printer.
Nothing is uploaded — the rotated file is generated on your device.
Most viewers rotate only the view. This tool writes the rotation into the file so it's permanent.
No — the rotation is applied in your browser.