In the Page Tab click on Background.
Choose which pages need a new background. Click on the button reflecting the range you’d like to use.
You can choose a color and click Ok to save your choice.
Alternatively you can choose an image file to use as the background for your documents. Click on Picture. You will see the bottom portion of the window change. Click on the … next to Select Picture to Browse your computer and select an image file.
Once you have added the image it will appear in the preview section in the bottom right corner.
Click on OK at the bottom to change the background.