you’ve got the option to insert an image watermark or a text watermark.
The watermark can be any image or text you want.
With the document already open, go toInsert>Watermark.

SelectImagefrom the side panel, and thenSelect Image.
Use one of the available tabs to choose an image.
Optionally adjust the watermark tweaks.

Here’s how to make a text watermark in Google Docs.
Go toInsert>Watermark>Text.
key in the watermark text into the box.

Optionally adjust the font style, transparency, angle, and placement of the text.

