There is no legal, free download for the base game's pk4 files (such as pak000.pk4 through pak004.pk4 ), as they contain copyrighted commercial assets. To obtain them legally, you must own a copy of the game from which you can extract or copy the files:
The engine reads these files alphanumerically. If two files contain an asset with the same name, the file that comes later in the alphabet (e.g., pak999.pk4 vs pak000.pk4 ) will override the earlier one. Steam Community Doom 3 Pk4 Files Download
Because the game assets are copyrighted, there are no "official" free download links for the base game files. You can acquire them by: There is no legal, free download for the