Adobe wants you to purchase Acrobat to be able to do that. Their strategy is to give you Reader for free, but for authoring they want you to buy their software.

Adobe wants you to purchase Acrobat to be able to do that. Their strategy is to give you Reader for free, but for authoring they want you to buy their software. However there’s also third-party PDF software one can use for that. And apparently Google Drive supports it too: https://www.wikihow.com/Attach-a-File-to-a-PDF-Document https://www.wikihow.com/Attach-a-File-to-a-PDF-Document