To copy a scene from one video to another in Synthesia:
Open your video and locate the scene you wish to copy on the left hand scene menu.
Right click on the scene and select the copy option or use the keyboard shortcut Command-C (on Mac) or Ctrl-C (on Windows) to copy the selected scene.
Open the video where you would like to paste the scene.
Use Command-V (on Mac) or Ctrl-V (on Windows) to paste the copied slide onto the scene bar of the destination video.
Notes:
The pasted scene will contain all of the same elements, animations, and script content of the source scene.
For other keyboard shortcuts available for your scenes see: Scenes Keyboard Shortcuts documentation page.