Now basically you need to download a custom mission, unzip it (as in most cases the files been archived) and then copy the new files into your HD2 main directory.
HD2 main directory by default (64-bit Windows) is located here:
DetailedIf you have sucessfully unzipped the mission files you should have got following folders
To check if you have all done correctly you're folder structure should look like below.
C:\\...\Hidden & Dangerous 2\Missions\MISSION_NAME (contains scene.4ds, actors.bin, scene2.bin, tree.klz, ...)
C:\\...\Hidden & Dangerous 2\Scripts\MISSION_NAME (contains .scr files)
C:\\...\Hidden & Dangerous 2\Models\MODEL_NAME.4DS
C:\\...\Hidden & Dangerous 2\Maps\IMAGE_NAME.BMP
C:\\...\Hidden & Dangerous 2\Sounds\SOUND.WAV
Additional files like .txt files as the ReadMe you don't need to copy. However if you want to play a custom mission
on your own server then you have to update your mpmaplist.txt file which is in your HD2 main directory.
Update maplist tutorial