Scanned documents are the main source of this problem. You scan a stack of papers, open the PDF, and half the pages are rotated 90 degrees because you fed them through the scanner slightly differently. It's one of those small annoyances that takes far longer to fix than it should.
How to do it
Go to pdfmerger.io/rotate. Upload your PDF. You'll see thumbnails of every page. Click the rotation arrows on any page to rotate it 90 degrees clockwise or counterclockwise. The thumbnail updates as you go, so you can see exactly what you're getting. Click "Save" when you're happy, then download.
You can also rotate all pages at once — useful when the entire document came through sideways from a landscape scan.
Which direction to rotate
If a page is sideways with the top pointing right, rotate it counterclockwise once. If the top is pointing left, rotate clockwise. If it's upside down, rotate twice in either direction (180 degrees total). The thumbnail updates immediately so you'll see it click into the right orientation.
The rotation only applies to the downloaded file
The original file on your device is never modified. The rotation is applied only in the new PDF you download. So if you accidentally rotate something the wrong way, just re-upload the original and start again.
Does it affect quality?
No. Rotating a PDF page changes the page's rotation metadata — it doesn't re-render or recompress anything. Text, images, and graphics are completely unaffected.
When the content is rotated but the page is fine
Sometimes you'll open a PDF where the content appears sideways even though the page size is technically correct. This usually happens when someone scanned a landscape document on portrait settings. Rotating the page in the tool fixes it.
But sometimes a document genuinely has landscape pages — for charts, tables, or wide diagrams — and those pages are supposed to look sideways in a portrait PDF viewer. In that case nothing needs fixing. Try printing a page to check before rotating the whole document.
Tip
If only certain pages are sideways and others are fine, use the individual page rotation controls rather than rotating the whole document. The thumbnails make it easy to spot which pages need fixing.