Now that I am using Preview instead of Adobe Reader, I am having trouble saving documents. There is no Save As… feature in the File menu!
You’re not alone in confusion! Apple replaced Save As… with Duplicate.
There is a good reason for it: Mac apps — the good ones at least — now save automatically, all the time. They even remember versions of themselves (File > Revert).
So now, you can make a copy by going to File > Duplicate, then File > Save. Also, as always, option-drag and copy/paste still work in the Finder.
Apple has a nice write-up of the feature in this article.
But it still feels weird not to have Save As!