there are two ways:
- You can export an image version with "File > Export > Version" and set the "Export Preset" to "Edit" in the export dialogue. Then add a watermark to this export preset, like this:
Or install the BorderFX plug-in. This plug-in allows to annotate image files with watermark images or captions. You can either add the watermark to the border or directly on the image.
You can download BorderFX here: BorderFX - BorderFX