Your PDF viewer has a rotate button, but it only rotates the page on your screen — close the file and reopen it, and the page is sideways again. If you need it fixed for good, in the file itself, that’s a different tool.
Go to the Rotate PDF page and add your file, up to 25 MB. Every page shows as a thumbnail — rotate individual pages that are sideways or upside down, or rotate the whole document at once if every page came out the same way. Download your PDF, and the rotation is saved permanently in the file; it opens right-side up in any PDF viewer, on any device, from now on.
Why this happens
Almost always the cause is a scanner: a page fed in landscape when the rest were portrait, or a duplex scanner flipping every other page. The scan itself is fine — it’s just oriented wrong, and rotating it is a cosmetic fix, not a re-scan. Both one page and the whole document are supported from the same view: if only a couple of pages came out sideways in an otherwise normal document, rotate just those; if the entire file is rotated, do the whole thing in one action instead of page by page. How to Rotate Only One Page in a PDF goes into the single-page case, including when a landscape page is meant to be landscape and shouldn’t be rotated at all.
After rotating: reorder the pages too, if they’re also out of sequence; crop the margins if a scanned page also has a border or wide margin worth trimming; OCR the document if it’s a scan and you want the text searchable; or compress it before sending it on. Rotating, reordering, and deleting in the same sitting? Edit PDF does all three from one screen and one download.
Rotate them with the free Rotate PDF tool — no account needed, no watermark added, file deleted the moment you download.