Rule 903 Subscribing Witness’s Testimony

If a document needs a witness to sign it (like a will might in some cases), that alone doesn't mean you have to bring that witness to court to prove the document is real. You only need to get testimony from that witness if the law that controls whether the document is valid actually requires it.

In other words, most of the time you can prove a document is authentic using other kinds of evidence, even if someone signed it as a witness. The only exception is when a specific law says a witness must testify to make that particular type of document valid. If no such law applies, you're free to authenticate the document some other way.