well, first of all, you do it in photoshop, but ps stock doesnt comee witht he .dds file format, the .dds file format is an Nvidia createion, and as far as i know they DO NOT offer it for download anymore, it was still up a few months ago..but i cant find it anymore, but luckaly i have a copy..so yeah, u cant open / edit the .dds file unless you have the plugin
You could also use Paint Shop Pro (which in my opinion is better than PhotoShop). You will still need the DDS plugin though. Get Paint Shop Pro 7 at http://www.JASC.com or Adobe Photoshop at http://www.ADOBE.com. Then once those are downloaded search for serial numbers on the internet, or just buy the full version.