Copy d3xp/pak000.pk4 (from the install CD)
and  d3xp/pak001.pk4 (from patch 1.3.1) here.

(Or copy dhewm3.exe and all the DLLs from the parent folder to your existing,
patched Doom3 installation)

See https://github.com/dhewm/dhewm3/wiki/FAQ#which-game-data-files-are-required
for more details.

The md5sums and sizes of those files are:
pak000.pk4 : a883fef0fd10aadeb73d34c462ff865d 514MB
pak001.pk4 : 06fc9be965e345587064056bf22236d2  98KB
