Word is designed to initially open documents at maximised screen. Sometimes documents will start opening in a minimised window. This might have happened by an unusual program glitch that set and saved operating data, or the boundaries of the document window were set outside of the screen's range in a previous session and got saved. Word can be initially maximised again by following a few steps.
Click the "Start" Windows and select "All Programs." Select the "Microsoft Office" folder.
Right-click the Microsoft Word program icon and select "Properties." A new window will appear with options specific to Microsoft Word.
Click on the tab labelled "Shortcut." There will be a field labelled "Run" with the options of Maximized, minimised, and normal window. Select the "Maximized" option. Click "OK" and the properties window will close.
Close Word if it hasn't been closed and restart. The program should now open all documents in maximised windows.
If this does not work for some reason, refer to references at Microsoft Support. There is another option configuring the program Registry, but it is not recommended. A Registry error can damage the program so it would be done at your own risk.