If you want to make the line spacing single, as it was in earlier versions of Word you can do so. In Word 2007 and 2010 the process is relatively easy. Click the Home tab, then select Change Styles. In the menu select Style Set, (first option), then click on Word 2003. Then select Set as Default and every time you open Word 2007 or 2010 you will see single spacing. Word 2013 is more involved.
To do the same in Word 2013 you need to click on the Home tab and then click on the No Spacing Style block, (located just above the Styles heading). Make sure that option is selected, then click the small down arrow in the lower right corner of the Styles ribbon. Click the Normal option. Then click the down arrow on the right side and select Update Normal to Match Selection. Right click the block Normal and select Modify. At the bottom of the screen select the radio button New Documents based on this document. Close Word and open again. It should keep the new settings. Done.