You can often download the MP3 audio files for free and legally by creating a basic account on the Difusión website . How to Use the Digital Version

While there is no single "official" free PDF for the complete Aula Internacional Plus 3

The official e-book version is DRM-protected but fully verified. You can read it on any device, highlight text, and sometimes use integrated dictionaries. Search for "Aula Internacional Plus 3" directly in your region’s store.