Is this really how I can add a custom pdf to a record like customer and then print a custom pdf from saved search results or advanced pdf generated from a saved search? https://leftledger.com/blog_addbutton.cfm

yes, if you want it to be generated on demand, this is the way. Really to do anything in the UI where you need access to server side only suitescript modules. 1. UE script before load creates the button 2. Client handles the button click and calls suitelet 3. suitelet does the heavy lifting on the server side if you don't need the on demand aspect of this then depending on your trigger/cadence you can just do this all in a single UE Scheduled or MR script.

Thank you.