I hope someone here knows what a Powerbuilder composite datawindow is and
can be more specific, but in essence Word 97 should be able to get data from
a. certain kinds of plain text file, which you would have to export from
Powerbuilder
b. certain kinds of common file-per-table database formats such as .dbf
c. ODBC drivers, which can typically only get data from structures that
have been stored to disk (or committed, in "proper" DBMS environment)

My guess is that these composite datawindows are ephemeral internal data
structures, in which case you would only be able to get at them if your ODBC
driver gave you some way to do it.