[DanielCoffey]

DDS is an image format so the only way to put text into it would be to "draw" the letters/words in something like Photoshop and save them as individual images. You could then put those pictures onto your model as though it was being painted on.

You can also save an image of the text with a transparent background then place that over the underlying texture. The texture underneath would show through.

This is what I had to deal with in Book Covers Skyrim. The titles and words on the cover were drawn on at the same time as the texture of the cover then saved as one solid image. The only way to translate them into other languages was to go back to the Photoshop file and redo the words then save the picture again.