So you want to edit LFS files that are in DDS format? Several textures in LFS are in DDS format including lights, interiors, track signage, seats, steering wheels and several other game and car components. To customise some textures in LFS You will need to edit the appropriate DDS file. DDS files can be handled by Paint Shop Pro and Photoshop after installing the DDS plugin which can be found here. Although these files are hosted by Nvidia, they are not GPU-specific, so you can use them with any brand card. You don't need all of the files shown on that site. You can download a DDS viewer which can enable thumbnails in windows explorer or my computer and view them easily. There are various viewers available and all seem to work well enough. Grab the plugin if you want to edit DDS with one of the programs mentioned above.
The DDS files can be found in your LFS/data/dds folder. There are a few things to be aware of before you begin:
*Once you have changed the DDS file all of the cars of that type will show that file, the texture is used universally. For example, if you customised the interior of the XF GTi, then all XF GTi's in your sim will have the customised interior. Unlike your car skin, these files are used on every car of that type.
*Be wary of texture size. Yes I know, you've got a fast PC and it can do anything except make your bed, but still be wary of texture size. The default textures in LFS work very well, replacing a 30KB texture with a 300KB texture will use more resources. It is very easy to overdo it so be sensible and back up your files first.
*When you save your customised file you will probably be presented with some complicated save options. Just try the default settings, in other words: don't worry too much about all the bells and whistles. If the option to generate mip maps is not selected then select it first but it should be on by default in most cases.
*There is a plugin that you will need and it works for Adobe Photoshop, Jasc.. (recently purchased by Corel) Paint Shop Pro only. Both of these programs use the same plugin file. There is a 3DS MAX plugin too, but MAX users check your version first to see if the plugin is even required.
Please note that DDS files use an alpha layer in many cases. If you don't know what that means I suggest you consult your software's documentation and try experimenting with the DDS format files.
Remember to save your files back into DDS format!
Finally, this is about all I know of DDS. It's also about all I know about Photoshop and Paint Sho Pro so if you post questions here that go beyond the scope of the info I have posted then someone else will have to provide the answers. You can find out much much more about DDS at this excellent site, just use their search box.