PowerPoint 2013 enables you to add one or more slides to your presentation from a different presentation that is either located on your computer or on a network without having to open the other file.
In the left pane where you see thumbnail images of your slides, click in-between the slides where you want to add the imported slide. A red line will appear as seen in the screenshot below between slides 4 and 5.
Now click on New Slides under the HOME tab and select Reuse Slides from the bottom of the list.
A new pane will appear on the right, which will ask you to locate the file you want to obtain the new slides from. Click Browse and then click Browse File in the drop-down menu that appears.
Once you locate the file, thumbnails of the presentation slides will appear on the right pane as shown below.
To insert one or all of the slides, right-click on any slide and select Insert Slide or Insert All Slides. You also have the option to apply the theme of the destination presentation to the imported slides by selecting Apply Theme to Selected Slides or Apply Theme to All Slides. To maintain the formatting of the source presentation, check the box Keep source formatting before you insert any slide.