Most social platforms (except LinkedIn and Facebook Groups) do not allow you to attach a raw PDF. You first need to host it to get a shareable link:
Use the "Share" button in Acrobat to create a public link that uploads the file to the Adobe Cloud for easy viewing. Download File x6qymvhfoi6h.pdf
If you want to show a preview of the file on visual platforms like Instagram or Pinterest: Most social platforms (except LinkedIn and Facebook Groups)