I-9 forms verify the identity and employment eligibility for employees hired in the U.S. The form is to be completed by both the employee and the employer (or authorized representative). As part of the process, the employee must present documents verifying his or her eligibility to work in the U.S., and the employer (or authorized representative) must physically examine these documents.
If you are being hired by a company who is out of the area in which you live/work, they cannot complete their part of the form. In that case, an Authorized Representative can examine your documents (typically a US Passport, or Driver License and Birth Certificate … the form instructions clearly show what documents are acceptable).
In this instance, I am not acting as a Notary, but as an Authorized Representative, so a notary seal is not affixed to the document.