A PowerPoint presentation's slide master contains the information about the presentation theme and slide layouts, including the background image, colors, fonts, effects and placeholders. To copy the background from one PowerPoint presentation to another, copy the slide master and paste it into the new presentation.
Open the source presentation with the background you want to copy. Create a new presentation or open the presentation to which you want to copy the background. Switch to the source presentation and choose View from the menu and Slide Master from the ribbon bar to view the slide master with the background image you want to copy.
Right-click the slide master and choose Copy.
Select View and then Switch Windows. Select the destination presentation to switch to that document.
Choose View from the menu and Slide Master from the ribbon bar.
Right-click the slide master and choose Paste. Select Close Master View to return to Normal editing mode in PowerPoint.