The mod may be intended for a different version (classic vs. BFG Edition) or may contain corrupted files. Remove the last PK4 you added and test again. Always keep a backup of your original base/ folder.
The base game relies on specific files ranging from pak000.pk4 to pak008.pk4 . The expansion, Doom 3: Resurrection of Evil , introduces its own set of files located in a separate directory. Why Search for New .PK4 Downloads? doom 3 pk4 files download new
If you're looking to download new PK4 files for DOOM 3, I assume you're interested in mods or custom content. Here's an interesting story: The mod may be intended for a different version (classic vs