Article 27 of Law of Evidence

A challenge on grounds of forgery may be directed against official and private instruments. Denial of handwriting, a seal, a signature or a fingerprint may be directed only against private instruments. The person challenging on grounds of forgery bears the burden of proving his challenge. Where a person denies that a private instrument originated from him, or swears that he does not know whether it originated from the person from whom he acquired the right, his opponent bears the burden of proving that it originated from him or his predecessor. If a party acknowledges the authenticity of the seal with which the private instrument was signed but denies having affixed it, he must pursue a challenge on grounds of forgery. Section Two Denial of Handwriting, Signature, Seal or Fingerprint and Verification of Handwriting