To combine two slideshow presentations, use the Reuse Slides option in PowerPoint 2010 and 2013. Reusing slides gives you the ability to specify where each slide should be placed. Note that imported slides adopt the theme in the recipient file.
Open the PowerPoint presentation that will be the recipient of the merge. Select the slide where you want the merge to begin. Imported slides will be placed after this selected slide. Click the Home tab and then click the words New Slide, directly below the New Slide icon.
Click the Reuse Slides option at the bottom of the drop-down menu. The Reuse Slides menu opens on the right side of the window.
Click the Browse button in the Reuse Slides menu. A navigation window opens.
Select a PowerPoint file on your computer or in your OneDrive storage directory. Click Open. Every slide in the file appears in the Reuse Slides menu.
Click the first slide that you want to merge into the open presentation. If you want the second slide to appear in a different location, choose a different thumbnail on the right of the window before clicking the second slide to be imported. When you have all of the slides you want imported, click the X in the Reuse Slides menu.
Change the order of the slides at any time by dragging the thumbnails.
Click on each slide that you imported. Make any changes needed, such as moving images or text boxes. When importing from one theme to another theme, the slide contents often shift and may appear outside of the slide margins. Just drag each object into its proper location, or resize an object by dragging a corner handle on its border.