[Manowar]

I have the files
myobject.dff
myobject.txd
myobject.col

How can I use a collision file?

[Baboon]

Open the kdffgui tool, load your myobject.dff and .txd files. Make a new collision, save it. Now a 'save' button should lit up next to source of the .dff file. Click it, save the model. And you're good to go.

The collision file is then stored in the .dff file.