declare long FindExecutable in "shell32.dll" ;
string lpFile, string lpDirectory, string @lpResult

* e.g:-

local buffer
buffer = space(2000)

result = FindExecutable("c:\test.rtf", "c:\", @buffer)

if result < 32 && failed
messageBox("No association")
else && Ok...
messageBox("Found " + alltrim(buffer))
endif