This has been asked before, on earlier OS versions, but doesn't seem to have gained satisfactory answers. I'm looking for a way to disable auto-save in Preview (only).
Background:
In OS X Lion, Apple introduced the concept of Auto-saving, Versioning and Restore (or Persistence, in which an application would reload the documents it previously had opened).
This works well for certain types of application, e.g. document-creation apps, but not for Preview, where users might not want to modify original images and PDFs, but rather to make changes to copies. It can also be easy to make accidental edits, immediately over-writing the original.
It used to be possible to prevent auto-save in Preview with the following Terminal command:
defaults write -app Preview ApplePersistence -bool no
However, this no longer seems to work, notably because Apple changed the default preference for all apps to close windows at Quit, instead of persisting on relaunch. Apple also seems to have split Auto-save and Persistence as two separate options, whereas previously they were intertwined.
I can of course set System Preferences > General to Ask to Keep Changes when Closing a Document. This works, but disables Auto-save on all applications. Checking this preference sets NSCloseAlwaysConfirmsChange in .GlobalPreferences from false to true. However, trying this key-value pair in Preview's own plist doesn't set the behaviour just for Preview.
In short: I'm asking if anyone knows a method which might disable auto-save only in Preview, without my having to lock all my original image files.
I guess it may be that I have to use some other image viewer and editor, though there aren't many that fill Preview's shoes, because Preview already exists. (The alternative is to knock up a read-only version of Preview in Xcode…)
Best Answer
Per Turning Off Auto Saving In TextEdit And Other Mac Apps on the "Mac Tricks and Tips" website:
Open System Preferences Go to "General" Enable "Ask to keep changes when closing documents"