To share content from CustomShow to a recipient who does not have CustomShow access, the most reliable way to keep content intact is to share a SlideShow to the recipient through a web link:
Content in CustomShow can be viewed in the Desktop Viewer App in a locally-downloaded format, and can also be downloaded to an iPad through the CustomShow iPad App.
The only option to export a presentation out of CustomShow as a local file in a commonly-used format is to print a presentation to a PDF. Any presentation or SlideShow can be printed to a PDF by opening the content, and choosing the Print option in the application in use. In all cases, the print dialogue will display a PDF button in the bottom left corner, which converts the slides to flattened images in a PDF.
Movie slides will not be exported in a playable format, as PDFs cannot contain movies.