To determine whether the content of "I signed by my handprint on blank paper is protected by law", the main judgment basis should be whether the content filled in later period truly reflects the objective facts and whether it is the expression of the signer's true meaning. Divided into the following situations:

The first is that the other person tells you what to fill in the blanks, and you willingly agree to the other person's request. If the content filled in afterwards is not only a fact, but also an expression of the true meaning of the signatory, it cannot be said to be illegal;

The second is that you are cheated or forced to sign. In this way, the content filled in afterwards is neither a fact nor an expression of the signer's true meaning. In principle, this is not protected by law. Of course, to prove that you have been cheated or forced, you need to provide witness or material evidence. Usually this kind of evidence is troublesome to collect, but it is really unbelievable that it is false. In this case, don't panic, you can consider the following practices.

1. If you are forced or realize that you have been cheated afterwards, you should report the case immediately and explain the details to the public security department for future reference.

If someone really cheats, extorts or sets you up with this label, you must be calm and calm. Because it is not true, there will be flaws or clues and other illogical places. Find these and let the law change you for justice.