2 clarify answer
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I found out https://discussions.apple.com/thread/5222408?start=0&tstart=0You can rotate inserts and annotations, like text boxes, rectangles or signatures, by arbitrary angles:

ROtateHold the Command ⌘ key and rotate the selected insert or rectangle or whateverannotation with your 2two fingers on the touch pad while pressing cmda trackpad.

Now whyAs far as I know this cannot be found in the Preview Help sectiononly works with trackpads and is another Microsoftismundocumented. It works on macOS High Sierra.

This is from an apple communities question: How can I rotate the text box in Preview

I found out https://discussions.apple.com/thread/5222408?start=0&tstart=0

ROtate the selected insert or rectangle or whatever with your 2 fingers on the touch pad while pressing cmd

Now why this cannot be found in the Preview Help section is another Microsoftism

You can rotate inserts and annotations, like text boxes, rectangles or signatures, by arbitrary angles:

Hold the Command ⌘ key and rotate the selected annotation with two fingers on a trackpad.

As far as I know this only works with trackpads and is undocumented. It works on macOS High Sierra.

This is from an apple communities question: How can I rotate the text box in Preview

1
source | link

I found out https://discussions.apple.com/thread/5222408?start=0&tstart=0

ROtate the selected insert or rectangle or whatever with your 2 fingers on the touch pad while pressing cmd

Now why this cannot be found in the Preview Help section is another Microsoftism