From : Blog Entry>>ILTA’s Blog Entry
PowerPoint Tips (Merge multiple presentations into One; Keyboard shortcuts when Presenting)   Merge Multiple Presentations into One There are times when you might want to   combine multiple presentations   into a single   presentation, such as when you want to add slides from an existing presentation to a presentation that you are creating. The best way to copy slides from one presentation to another is to insert them using the Slide Finder dialog box (Insert menu, Slides from File command). [More]