For real - We're In 2021!
Acrobat Pro cannot change the size of a PDF document.
Only way to do that is to print a PDF copy.
I want to just change the document size (i.e. A4 -> A5) in Acrobat Pro and save. That would be great!
I don't want to go back to PS, Illustrator or InDesign to do that. I don't wan't to print another PDF copy to do that.
Just open document settings > change size - voila!