A question from a client:
“I have a slideshow on my desktop, and I’d like to be able to play it on my laptop. What’s the best way to transfer the file(s) over to the laptop?  None of the images are on the laptop at the moment.  If I save the desktop slideshow as a PDF, I don’t think the music will go, nor can I replace it when I play it on the laptop.  Is that correct?”

My answer:
“Correct, from Lightroom, Exported PDF slideshows cannot contain music.

The best way to do what you describe:

1. On your main machine (in your master catalog etc.) put the desired files into a Collection, if they’re not already.
2. Right-click/control-click on the Collection name and choose “Export Collection as Catalog”. Choose your desktop as the location and give it a descriptive name. Also enable the option to copy the original (master) files.
3. Copy that folder, with the catalog and all the image files, onto your laptop. It will be easiest if you just copy the folder to the desktop (Finder or Explorer). Using a USB jump drive would probably be easiest for this.
4. On the laptop, open the new folder, and double-click the exported catalog to open Lightroom with that catalog loaded.
5. Set up your slideshow and play it from there.

NOTE: You will also need to copy your music file(s) to the laptop.

ALSO NOTE: This is one of those cases involving multiple catalogs where you will need to check next time you open Lightroom that the correct catalog is loaded, before you continue working!”