I would Like to know if Capture NX-D can add a watermark to my photos. I searched through the software and the help menu but didn't find any. Is this possible? If yes, how?
No. The feature is not available in NX-D.
In Capture NX and NX2, according to nx101.com, while there is no built-in watermarking functionality, you can "fake" your way to a watermark by using the brush tool to draw a watermark, then blend it to your photo. You can then save the steps as a custom action so you could apply it to any other photos. It's slightly "hackish", but that's the best that can be done with those tools. But even that capability is not present in NX-D.