You can insert slides from another presentation into the current presentation. You can also copy and paste slides between presentations.
Open a presentation, and choose View - Normal.
Choose Slide - Insert Slide from FilePage - Insert Page from File.
Locate the presentation file containing the slide that you want to insert, and click Insert.
Click the plus sign next to the icon for the presentation file, and then select the slide(s) that you want to insert.
Click OK.
Open the presentations that you want to copy and paste between.
In the presentation containing the slide(s) that you want to copy, choose View - Slide Sorter.
Select the slide(s), and then choose Edit - Copy.
Change to the presentation into which you want to paste the slide(s), and then choose View - Normal.
Select the slide that you want the copied slide to follow, and then choose Edit - Paste.