If you're using Office 2008 I'm afraid not - unless someone has an
AppleScript that will adjust window size and/or position. In prior versions
you can create a macro to do it, but 2008 doesn't support VBA.
Keep in mind, though, that a doc will reopen in the same way it was last
saved, so what you're experiencing may only be temporary. Once you've opened
an existing file & adjusted the window, make some other change to the
content - even if you then undo. Save the file & that's how it should
reopen. Files you receive from others you can't control until after you open
them for the first time.