How can I set default setting for line spacing when opening a Microsoft Word document?

Solution 1:

Go to Styles in the Home Ribbon and change the Normal Style to "Single spacing" or as you wish spacing to be.

Make sure you select the option in Styles to apply to all documents. Be sure to save the document so the style is changed.

I set Word for Single Spacing within a regular paragraph.

Please see the screen shot below.

You can also set the Font (in the Home Ribbon) and set spacing in Advanced Properties. Then set the Font as Default for all documents.

Word Normal settings