To add an audio file to a publication page:
Open your publication in Edit mode.
Use the navigation arrows at the bottom-left of the editor to go to the page where you want to place the audio file.
Click the Sound tool on the left toolbar.
Click Upload to use a file from your computer, or Select from Library to use an audio file already uploaded to your Library.
Note: To have the audio start playing automatically when the page opens, enable the Autoplay option.