Unauthentic (adjective)

1. Not genuine or real; not of the original or true source.
2. Not being in accordance with the facts.

Origin:

Un- + authentic.

Examples:

1. The painting was discovered to be unauthentic and a forgery.
2. The food at the restaurant was unauthentic and did not taste like the original dish.
3. The unauthentic signature was not made by the original author.
4. The unauthentic document was not a original copy.
5. The unauthentic product was not made by the original manufacturer.