Microsoft Office PowerPoint allows you to insert slides from another presentation. It doesn't have a way to merge a custom show from one presentation to the other after you have inserted all slides from that presentation. You need to create the custom shows again in the new presentation. This is where Custom Show Merge Assistant of ProTools for PowerPoint proves useful. The Custom Show Merge Assistant recreates the custom shows in the new presentation after you have inserted all slides from another presentation.

You need to do the following:

1. Open your source and target presentations. You insert slides from a source presentation into a target presentation.
2. Note the total number of slides that are present in the target presentation before inserting slide into it from a source presentation.
3. Insert slides from the source presentation into the target presentation through Microsoft Office PowerPoint at the end of slides in the target presentation.

4. Run Custom Show Merge Assistant from the Insert tab in Microsoft Office PowerPoint 2007 or the ProTools menu in Microsoft Office PowerPoint 2003 or older versions.

You will be presented with the following dialog box:

You need to select the source and target presentations in the appropriate dropdown boxes. Provide the Custom Show Merge Assistant with the number of slides that existed in the target presentation before inserting the slides from the source presentation. Click Merge Custom Shows button to merge the custom shows from the source presentation to the target presentation.