Thank you for your post.
Does the crash only occur with this one file? That is, if you create a new database file, and create a button to launch Microsoft Word application, does it work as expected? This will let me know if it is file specific or application specific.
If the same issue occurs, create a new user account, launch FileMaker Pro, create a new file and create a button to launch Microsoft Word. This will let me know if it is the user account or application.
Since this worked previously, what has changed in your system environment?
Any other information you can provide may be helpful.
What method are you using to launch MS Word?