Board Administrator - File watermarking (add-on)

Click on your profile picture in the top right, then select "Settings":

Navigate to "Boards" via the left-hand column, then click on the board for which you want to enable the watermark option:

Under Documents > Watermarking, you can activate the watermarking option for your board, set its opacity, and activate document flattening for a higher security level:

Note: With the first flattening option activated, downloaded files then can't have their text selected, searched, or copied.