Try this - you'll need to choose a suitable document name (e.g. test.wpd) and make sure that buffer genuinely contains xxx.exe (the program you are looking for - .wpd might be associated with someting else)

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

buffer = space(2000)
result = FindExecutable("c:\test.doc", "c:\", @buffer)
if result < 32
messageBox("** FAILED **")
else
messageBox("--- success --- [" + alltrim(buffer) + "]")
endif