Notary services in California are available to help you with signing contracts, power of attorney, wills, affidavits, deeds, and other common legal documents. The fraud deterrence provided by a Notary helps all parties entering into a legal agreement stay protected and avoid bad outcomes.
Always check with your selected Notary service prior to your visit to ensure any specific requirements for your state are met. In general, the following things are needed:
Notaries can charge a nominal fee for each signature, the maximum of which depends on the state. Typical price range is anywhere from $2-$20. Check with them ahead of time for exact costs.
Check with your notary ahead of time, but government issued IDs including Drivers Licenses, Passports, Military ID, Green Cards are commonly accepted. Make sure it has a photo, and remember it's at their discretion to refuse to notarize if they aren't convinced of your identity.
Some documents require a third party witness to the signing, but not all. Rules again vary by state, so check with your Notary on whether a witness is needed and any specific requirements. Generally speaking it will need to be someone with no interest in (not mentioned in or otherwise impacted by) the agreement outlined in the document. Friends and neighbors are a good bet.
As with all things, check with your Notary ahead of time to make sure they're comfortable with it, but in general it is possible. It's important that the person signing be able to communicate with the Notary, but there's no specific requirement that the Notorizing agent be able to read the document itself.