I opened a pdf in macOS today.
It was opened in the default pdf viewer and I could scroll through the pages. Then I accidentally dragged one of the pages in the left area where all of the pages are shown as thumbnails. I was surprised that I can do that, because surely I was just viewing the pdf. Like in a pdf viewer. Like read only.

Imagine my surprise when I closed the pdf, opened it again and found the pages in the wrong order!

It freaking autosaved my accidental drag and drop in the standard app that opens pdfs!
Who the hell thought it was a good idea to do that? That’s insane!