Watermark Lab

Watermark Lab lets you stamp any PowerPoint, Word or video file with a customisable diagonal text watermark in seconds. It runs entirely on your Windows machine — no cloud, no subscription, no data leaves your device.

PowerPoint and Word files are watermarked natively — the result is a real, editable document, not a flattened image. A true-render live preview shows the genuine watermarked output as you type and adjust settings. Video files are processed with ffmpeg, which the app downloads automatically on first use. The app ships as a self-contained portable folder — unzip and run, no installer needed.