Zork "not an adventure game file"

After downloading Zork from GOG, the DATA file which is ZORK1.DAT will not load in other interpreters,
I’m getting “not an adventure game file” as an error message in Gargoyle.

Are GOG versions of ZORK and other infocom games sort of locked, and prevented from being able to be played?

Solved this by changing the extension to Z5.

Sorry, can’t delete this thread, but I answered it.