Hello. First of all, this behavior is illegal. If your boss uses this contract to defraud the country, your company or other company units, it is a criminal act. 400,000 is at least a huge amount in criminal law. If it is a crime, you are the perpetrator. As for whether you are an accessory or a principal, you cannot tell now. After all, you are an adult, so he probably did not force you.

Of course, it may not matter if your boss uses this contract to cheat on his wife. But it can also be a crime.

Also, if the seal is that of another company or state agency, it falls under the crime of forging company or enterprise seals under Article 280 of the Criminal Law. This is very important. The criminal law does not stipulate the amount of the crime, which means that if you do this behavior, it may be a crime. Of course, it still depends on the behavior your boss performed to determine whether it is a separate conviction, absorbed by the previous behavior, or something else.

Of course, if your boss only sees it himself, that’s okay. In short, if he uses that thing to deceive people, he will commit a crime. Because you said that the contract was fake, and in common people's words, it was a lie.

It is recommended that you immediately ask your boss what the purpose of using this is. At the critical moment, you have to judge whether he wants to do something illegal. If so, it is recommended that you call the police.

I hope my answer will be helpful to you, and I hope you will protect your rights.