macOS utilizes a system-wide feature called “Versions” or “Auto Save.” Unlike traditional operating systems where you must manually press Ctrl+S to save your work, macOS applications like Preview constantly save your changes in the background. If you open an image in Preview, use the markup tool to draw a red circle on it, and then close the window, Preview will automatically overwrite the original image file with your edits without ever asking for confirmation.
For many users coming from Windows, this behavior is absolutely infuriating. If you simply wanted to test out an edit, crop a photo temporarily to see how it looks, or resize an image without intending to destroy the original high-resolution master file, the auto-save feature will irreversibly overwrite your original data the moment you hit the red close button.
You can force macOS to behave like a traditional operating system, requiring explicitly granted permission before it overwrites an existing file.
How to Stop macOS from Auto-Saving Edits
You must change a global setting within the System Settings to restore the “Save As…” prompt.
- Open the System Settings (or System Preferences) via the Apple Logo in the top-left menu bar.
- Scroll down the left sidebar and click on Desktop & Dock (or General on older macOS versions).
- Scroll down the right pane until you find the section labeled “Windows.”
- Locate the toggle switch labeled Ask to keep changes when closing documents.
- Turn this toggle to the On (blue) position.
The behavior of Apple Preview (and Pages, Keynote, and Numbers) will instantly change. If you open a photo, make an edit, and click the red X to close the window, Preview will pause and display a dialogue box warning you that you have unsaved changes. You will now have the power to click “Revert Changes,” ensuring your original master file is perfectly preserved.