How many times have you started a PowerPoint presentation and then realized you needed to use a different template? Fortunately, there's an easy way to copy over the theme from one presentation to another.
This works in both PowerPoint 2007 and PowerPoint 2010. First, open both your source and destination documents (and close any others if more decks are open). Go to the View menu and click the Arrange All button so you can see both at the same time:
Now, select the source deck (pictured at right below) and then click on the thumbnail of the slide you want to copy the theme from. Once selected, click the Format Painter icon directly above it on the Ribbon:
Now click on the destination deck and then click the thumbnail of the slide you want to receive the theme:
You may need to click twice: Once to select the target deck and a second time to apply the format to the thumbnail.
This technique works best if you use it on a new presentation, since all new pages will be based on the new theme. But you can apply the format to all slides of an existing presentation if needed. Just double-click the Format Painter button before selecting the destination deck and then click on each of the slide thumbnails individually to apply the theme.