This is not a UI, but rather a set of window templates that give almost any UI using the default templates a similar look to the PDA in Doom 3. Great way to cover up those un-modded default windows with something that at least looks nice.
To use these templates:
If your currently using default:
Extract the zip file to a new directory called DoomPda. Then in game go into options -> general -> Load UI Skin -> DoomPda, hit ok.
If you want to use it with another UI:
Check the folder of the UI your using it with for EQUI.xml. If it contains one, add
above the entry for EQUI_Animations.xml. Then extract all except for EQUI.xml from the zip file. If your UI doesn't contain a EQUI.xml, just extract the zip file into it's folder.