Grand Theft Auto: The Trilogy — The Definitive Edition works on both old Renderware and new Unreal engines. The latter uses archives for its game files (.pak). If you want to install a mod for the remaster, you have to create your own .pak file with updated files in it. Here's the quick way to extract files from game.pak and the instruction on how to create own .pak files.
How to extract game files from GTA: The Trilogy — The Definitive
Edition
Download Umodel app and start umodel_gta_trilogy.exe.
Click on "..." button to choose the folder. Find a .pak with game files (You can find GTA: San Andreas archive here: GTA San Andreas - Definitive Edition / Gameface Content / Paks). You'll see the archives structure. Click on Tools button and select Options.
This window allow you to choose some extraction and save options. We recommend to set the options similar to the screenshot. Click OK.
To extract a file, just select it the list and click Export. You will be asked to select Unreal Engine version. Select 4.26 and click OK. The example below shows the extraction of SM_colt45.uasset file, that could be find in Game / San Andreas / Weapons. This file could be imported to Blender and extracted to .OBJ.
How to make .pak for GTA: The Trilogy — The Definitive Edition
So you've modded a file and now you want to add it to the game? You will have to create your own .pak file. Download UnrealPak app from the GitHub. After installing type a command line with the code:
Test.pak - the archive that will be created; dataToPack.txt - the file that will be archived to your .pak. Just remember to edit the path to UnrealPak.exe and the path for your new .pak.
Beware that the structure of your .pak should be exactly the same as in the original game.pak. The mod won't work if you change the structure. To check the structure just unpack the game.pak.
Tips for finding game files
Textures from gta3img usually are in San Andreas Textures
gta3 (with own categories);
The magnifying glass icon in the top bar of the app is a
search for a file in the folder you're currently in. It doesn't
search in subfolders.
GTA: The Trilogy — The Definitive Edition files types
Prefixes will help you to understand game files types:
Textures starts with T_
Static models are SM_.
Materials examples are MI_
There are suffixes for textures:
_BC - diffusion maps;
_N - normal maps.
There are additional suffixes that we will cover later.