GA can track visitors from all referrers, including search engines, display advertising, pay-per-click networks, e-mail marketing and digital collateral such as links within PDF documents.
GA can track visitors from all referrers. This is including search engines. Search engines are display advertising. Display advertising is pay-per-click networks. Display advertising is pay-per-e-mail marketing. Display advertising is pay-per-digital collateral such as links within PDF documents.