I had never thought that it would take my complete day to put a background image in word. Initially, I have used background image, everything looked well and fine. I got into trouble when I printed it to PDF, using PDF printer. I saw background image is tiled.
I goggled it, saw many people having same problem. I have gone through many posts, but had no luck to solve this.
Finally, I found work around for it. Here it goes.
1. Insert > Header > Edit Header, cursor will appear in your header section.
2. In Tool Bar, you will see "Picture" icon, click on it and select the background you wanted to put.
3. Then go to "Text Wrap", choose "Behind the text".
4. Now adjust the background image, according to your need.
Now you can print it, it will be same as what you see.