Q. Can a notary also witness documents being signed?
A.  Any individual over the age of 18 can be a witness to a document signing or Will signing.
 
Q.  Can a notary charge for acting as a witness?
A.  If acting as a witness is an official notary act in the state where the notary is commissioned or acting, then they can charge whatever their state’s maximum appointed fee is.  In all other states where witnessing is not an official notary act, then the notary can charge whatever the client will agree to.
 
Q.  Should I hire a notary to act as a witness?
A.  You can if you like, but unless you need some special documentation done, that only a notary can perform, there is no real need to have a notary around.
 
Q. Can you recommend some more detailed reading materials about this topic?
A.  Yes, please read:  Can a notary be a witness?

Q. When is a Notary required to witness signatures?
A. Jurat Notarizations require the Notary to have the signer sign before them. A handful of states require the Notary to witness Acknowledged signatures as well.

Tweets:
(1) Any individual over 18 can witness documents being signed, including a Notary Public.
(2) Can a notary charge for acting as a witness? Yes, but your state might have a maximum charge.

You might also like:

Can a Notary act as a witness?
http://blog.123notary.com/?p=21359

Credible witnesses from A to Z
http://blog.123notary.com/?p=452

Fraud and Forgery related to the notary profession
http://blog.123notary.com/?p=2294