Rotating a PDF does not re-encode anything
Every page in a PDF carries a /Rotate value — 0, 90, 180 or 270 — that tells a viewer which way up to draw it. Rotating a page here changes that number and nothing else. The text stays text, the images keep their original compression, and the file size barely moves.
This matters because the obvious alternative is not lossless. Printing a sideways document to a new PDF, or screenshotting each page and reassembling it, flattens everything: the text stops being selectable, the file usually grows, and the quality drops. If all you need is for page 4 to stop lying on its side, changing one number is the correct fix.
It also means rotation is instant regardless of document size. A 400-page scanned deposition rotates as quickly as a two-page invoice, because nothing is being re-rendered.
Why scanners produce sideways pages in the first place
Two things usually cause it. Sheet-fed scanners record the orientation of the paper as it went through the feeder, so a landscape page fed short-edge-first is stored rotated. And phone camera scans inherit the EXIF orientation of the photo, which some apps write into the image and then ignore when they build the PDF.
Both produce a file where the pixels are fine and only the orientation flag is wrong — exactly the case rotation fixes cleanly. If instead your page looks stretched or the text is mirrored, rotation will not help, because something has gone wrong further upstream in the scan itself.
Mixed orientations in one document
Reports that mix portrait text with landscape tables are common, and they are the reason this tool works page by page rather than document-wide. Select just the landscape pages and turn those. The thumbnails make it obvious which is which without opening the file in a separate reader.
While the pages are on screen you can also reorder them by dragging, delete the blank separator sheets a feeder inserted, or duplicate a page you need twice. All of it happens in the same grid, and every step is undoable with Ctrl+Z before you download.
What rotation cannot fix
It cannot deskew a page that was fed in crookedly — a scan that sits at four degrees needs re-scanning or a raster correction, not a 90-degree turn. It cannot change the paper size or crop the page box. And it will not help if the original scan cut off an edge, because the missing part was never captured.
It also does not change how text flows. A landscape page turned to portrait is still a landscape page displayed upright: the content keeps its own proportions inside the rotated frame. That is the correct behaviour, and it is why the result prints exactly as it looks here.