I've already done the work and measuring for you -- just make sure you DO NOT scale the file when printing, and they should fit perfectly. Cut out along the darker outer line, and your text should not go outside the lighter inner line (this is where the "window" should be).
Simply open the file in Adobe Reader and click "Highlight Fields". All editable fields should then turn blue. Use your cursor to make the field active and type your text. "Ctrl" + "E" will bring up the properties tool palette and you can change font, color, size, spacing etc. If you want your text centered vertically and/or horizontally, click "More" in the properties tool palette and then the "Paragraph" tab.