What turning a page really does
Every page in a PDF carries a small number that says how a viewer should turn it before showing it: 0, 90, 180 or 270 degrees clockwise. It is called the page's rotation. Turning a page here means changing that one number. The text, the pictures and the drawing instructions of the page are not opened, redrawn or compressed again, which is why a scan stays exactly as sharp as it was and why even a large file is done almost at once.
An existing rotation is added to, never replaced. A page that is already turned 90 degrees and gets another 90 ends at 180, and one turned 270 that gets 90 is back at 0. This also works when the rotation was not stored on the page itself but inherited from the document, which some programs do. Viewers and browsers apply the rotation when they show the page, and printing from them follows it.
Many viewers have a rotate button that often only changes your own view and is forgotten when you close the file. Here the rotation is saved in the file, so it stays right for everyone you send it to.
Sideways scans, upside down backs and mixed pages
The most common reason to rotate a PDF is a scan that came out sideways because the sheets went into the scanner the other way round. Leave All pages on and turn them once. If only some sheets were fed differently, use the preview to tick the sideways pages and turn just those.
Double sided scanners sometimes return every back side upside down. The backs are the even pages, so choose Even pages and press Upside down 180°. The other way round, when the fronts are the problem, choose Odd pages.
Documents that mix portrait and landscape pages are harder to read on a screen. All portrait turns a quarter right every page that is wider than it is tall, and All landscape does the opposite. Pages whose two sides differ by less than half a percent count as square and are not touched, because there is no right way to turn them. The helper always turns to the right. If a page ends up with its text upside down, give that page its own 180°, or press Reset and do it by hand.
Turns are limited to quarters. A PDF can only store 0, 90, 180 or 270 degrees, so this tool cannot straighten a page that was scanned at a slight angle.
What the new file keeps
Because the file is edited and saved again rather than put together from copied pages, everything that is not a page's rotation stays as it was: bookmarks, links that jump inside the file, links to websites, comments and highlights, fillable form fields and what has been typed into them, page labels such as roman numerals, layers, accessibility tags and the title, author and other properties. The page content is byte for byte the same as in your file.
Two things do change. Saving writes the whole file again, so a digital signature on the document stops being valid, as it would after any edit. And the file is packed again, so its size moves, usually by a small amount. A file whose small objects were not packed before can come out clearly smaller.
A PDF that is protected with a password or with permission settings is encrypted, and ClipLime cannot decrypt files. It is refused with a message instead of producing a broken result. If you are allowed to, open it in a PDF viewer, print or export it to a new PDF without protection, and rotate that copy.
Big files and your device
The file is read into your browser's memory, which needs several times its size. ClipLime warns you when a file is large for your device, which is around 60 MB on a phone and a few hundred megabytes on a computer. A single file above 1 GB is refused. If your browser runs out of memory, nothing is lost and nothing was sent anywhere: close other tabs and try again, or use a computer.