When you have several documents opened, there is a better way than using the minimize and maximize buttons. Pressing and holding down the CTRL button and pressing F6 will allow you to toggle between the opened files.

Another way of navigating between opened files is through the Window option located on the Menu Bar. Click on Window and a drop-down menu will appear. A list of documents will appear at the bottom with a check mark next to the active document. To change the active document, just click on a different document.