There are no specific procedures to challenge the authenticity of an authentic instrument. The content of the party statements included in the authentic instrument may be contested by providing counter-evidence. Should someone dispute the authenticity of an act, he/she must provide evidence that either the act is forged or that the person creating the act was not entitled to do so. There is no difference in this regard between challenging the authenticity or the material validity. If the challenge is successful, the authentic instrument can no longer be enforced. The actual enforcement may be challenged by way of an ‘enforcement dispute’.
Within what timeframe: general rules apply, meaning within 20 years, see Art. 3:306 Civil Code.