How to Add a Watermark or Text Overlay Using Preview on macOS

When you are preparing to transmit a sensitive PDF document or a proprietary image (PNG/JPEG) from a macOS workstation, releasing the raw file without cryptographic attribution allows malicious actors to steal your intellectual property. To mathematically burn a persistent, un-removable copyright notice or “CONFIDENTIAL” overlay directly into the geometric architecture of the file, you must deploy the Core Graphics engine within the native Preview application to inject a Watermark.

Executing the Text Injection Matrix

The Preview engine utilizes a dynamic Markup Toolbar that allows you to spawn active geometric objects (text boxes, shapes) and permanently fuse them with the host file’s raster data.

1. Locate your target image or PDF file in Finder and double-click to open it natively in Preview.
2. Look at the absolute top menu bar. Click the View menu and select Show Markup Toolbar (or execute the hotkey: Shift + Cmd + A).
3. A secondary toolbar will spawn directly below the primary interface.

Deploying the Watermark Vector

4. Locate the Text Tool icon (a capital “T” inside a geometric square) within the Markup Toolbar and click it.
5. The engine will instantly spawn a text box containing the word “Text” directly in the center of the active file.
6. Double-click the text inside the box and type your absolute watermark string (e.g., CONFIDENTIAL – DO NOT DISTRIBUTE or © 2024 Your Name).
7. Click the Text Style icon (a capital “A”) in the toolbar. This opens a typography modal. Mathematically increase the font size (e.g., 72pt), select a bold typeface (e.g., Impact or Arial Black), and change the text color to a highly visible red or a subtle, semi-transparent grey.
8. Click and drag the geometric boundaries of the text box to position it strategically across the core content of the file, making it mathematically impossible to crop out.
9. Press Cmd + S to execute the save protocol. The exact millisecond you do this, the Core Graphics engine violently flattens the file, permanently fusing your text vector with the underlying pixel data, locking the watermark into the digital architecture forever.