Understanding the Preview App and the Duplicate file option I'm running macos Sierra with Preview 9.0 on an iMac. I have a fairly large (40 MB) pdf file that is a version 1.6 PDF. The Preview app does not have a 'save as' option. Your choices under the file menu are: save, duplicate, rename, move to, export, and export as PDF. 



Duplicate makes a copy but it converts PDF from version 1.6 to 1.4 and this in itself reduces file size from 40 MB to 20 MB. 'Move To..' and 'Rename' have no noticeable effect on file or size.  Export has several options. The 'None' option, however, also converts file to PDF 1.4 from 1.6 again reducing file size to 20 MB.  Export to PDF does the same but file size is 19.5 MB. I'm confused on these differences. It appears just going from PDF 1.6 to PDF 1.4 cuts file size in half. Why is this and why the conversion in 1st place. The only way I know to truly make a copy is do it in Finder using cntrl-c. What info has been lost in going from PDF 1.6 to PDF 1.4?
To get Save As... on the File menu in Preview, and many other apps as well, press the option key when clicking the menu.

The option key also modifies other commands on different menus as well.



Note that the shift key also modifies commands in some cases.