Can I be both a witness and the notary to a deed or other document?

Yes. The Courts upheld in Edwards v. Thom (25 Fla. 222), that being the notary to a transaction does not render you incompetent as a witness. However, if the pre-printed certificate requires the notary to take the acknowledgment of the witnesses or to swear in the witnesses, the notary may not also serve as a witness because this would cause the notary to notarize his own signature, which is prohibited by Florida law. Particularly with last wills and testaments, both the person making the will and the witnesses are sworn by the notary, therefore the notary could not also serve as a witness to a last will and testament.