And don't get me started on what a pile of crap Preview has become - trying to save a file under a different name now involves duplicating and renaming or exporting or some other nonsense - what was wrong with 'Save' and 'Save as'
Press <Alt> (aka <Option> on some keyboards) in the File menu and 'Save As' will appear.
Where Sierra's version of Preview has really messed up my workflow is taking away the ability to right-click on the filename at the top of the window and see where the file is in the directory tree - clicking on the parent directory would in prior versions highlight the file in Finder, making renaming a cinch.
Looking at that again as I type, it's plain buggy. Some documents currently open in Preview allow me to do that, others don't.