There are various ways to access an already created file however, specifically if currently is a microsoft office word document running and you want to use its window to open an existing word file then follow below guide.
- Simply press Ctrl + O keys on the keyboard or click the office button.
- click open command from the drop down list. (Notice an explorer window appears)
- In the file name box, type or select the name of the document to be opened.
- If the document is in another format, select a file type.
- Click the open button.
You could also click the open command on the quick access tool bar then follow the above steps from step three above.
Get more keyboard shortcut keys in Windows 7 from here