A family of Microsoft word processing software products for creating web, email, and print documents.
Word would work the same as any other app. You can use something like:
tell application "Finder"
open document "/Users/<you>/Desktop/myfile.docx" as POSIX file
end tell
You'll need to use the proper path to the file of course, but it's a simple matter of asking the Finder to open the file as you would yourself through a double-click.
I like the POSIX path because you can simply drag and drop the file in the Script editor to get the path in.
Corentin