GEOPAK-TIN FILE FROM A DTM FILE

Hello,

I am new to Geopak V8i SS2 and learning the corridor tools. 

I would like to make a *.tin file from a *.dtm file.  The DTM tools does not have an option to select a *.dtm file but only a *.dat file.  What is the best way to get a tin file from a dtm file?