How to rotate pages in a PDF and make it stick
View rotation and embedded rotation are not the same thing. Here is how to fix a sideways PDF so it stays fixed.
The most frustrating thing about a sideways PDF is that it seems like it should be a two-minute fix. Click something, save, done. But then you open the file on another computer and it is sideways again.
That happens because there are two different things that get called "rotation" in PDF viewers, and only one of them writes anything to the file.
Rotating to read vs rotating to save
Most PDF viewers let you rotate pages while you are looking at them. It is a display setting, the same way zooming in does not change the file. Close it, open it elsewhere, and it snaps back. Nothing was saved.
To actually fix a sideways PDF, the rotation has to be written into the file itself. That is a different operation and it requires something that edits and saves the PDF, not just changes how it looks on screen.
Rotating some pages but not others
A scan that came out sideways is usually consistently sideways, so rotating everything at once works fine. The trickier situation is a combined document where most pages are portrait but a couple of landscape pages ended up in the middle. There you want to select only those pages and leave the rest alone.
PDFShore handles both. You can pick individual pages in the thumbnail view or apply the rotation to all of them at once. Left 90, right 90, or 180 if the whole thing is upside down.
Does rotating change the file quality?
No. Rotation in a PDF is just a number stored in each page's metadata, not a transformation of the actual content. Text stays selectable, images stay at their original resolution, and the file size barely moves.
One thing to check first
Password-protected files need to be unlocked before you can edit them. Same for PDFs someone set as read-only before sending. If the tool says it cannot modify the file, that is usually why.