It says unknown identifier because you didn't define any of your variables. There is also something wrong with your DTM. It compiles fine, but it gives a buffer error when you try to run it. I tried a different DTM and it didn't give that buffer error.
Code:
program New;
var x,y,PickAxe,PickColor:integer; //DEFINE VARIABLES
begin
PickAxe := DTMfromstring('78DA633CC2C4C0E0C2C8800C38B918124813' +
'448F43F1030EE02AA8940552321C00CA661A28C97806ABC50D5C0' +
'005CCD0EA01A6754357CBC9CA86A8E01D538A0AA5157534151030' +
'0BC3C0A39');
if FindDTM(PickAxe,x,y,574,218,575,240) then
PickColor := getcolor(x,y);
FreeDTM(PickAxe);
end.