Short answer. Yes. Violence or intimidation annuls the obligation even where it was employed by a third person who took no part in the contract. You do not have to show that the other party made the threat, knew of it, or benefited from it. Strictly, the contract is voidable rather than void.
What the law says
Violence or intimidation shall annul the obligation, although it may have been employed by a third person who did not take part in the contract.
Civil Code, Article 1336 — Violence by a Third Person. Read the full provision →
Why a stranger's threat is enough
The law is protecting the reality of your consent, not punishing the other party. If you signed because you were beaten or frightened into it, your consent was not free, and it makes no difference whose hand held the threat. That is why this article expressly extends to violence or intimidation employed by a third person who did not take part in the contract. The innocence of the person you contracted with is not a defence, and you do not have to prove any conspiracy between him and the person who threatened you. The rule is deliberately different from that governing fraud by a stranger, which the law treats far less generously.
Voidable, not void — and the difference matters
The heading people search for is "void", but the correct term is voidable. The contract exists and binds you until a court annuls it in an action you bring. The other party may demand performance in the meantime, and rights that innocent third persons acquire in good faith before annulment can survive. Only the person whose consent was vitiated may attack the contract. Crucially, the right can be lost: ratification, whether by an express confirmation or simply by voluntarily performing or accepting benefits after the fear has passed, cures the defect and closes the door. Silence over a long period after you were free to act looks very much like ratification.
What counts as intimidation
Violence is serious or irresistible force. Intimidation is a reasonable and well-grounded fear of an imminent and grave evil to your person or property, or to that of your spouse, descendants or ascendants, that leaves you no real choice. Courts weigh the age, sex, condition and circumstances of the person threatened, so what would cow one person may not cow another. Two limits are worth knowing. A threat to enforce a claim through a lawful demand or a legitimate court action is not intimidation, however unpleasant it feels. And mere reverential fear — respect for a parent, an elder or an employer — does not by itself annul consent, though pressure that crosses into real fear may.
Acting on it, and the clock
Preserve the proof while it exists: police blotter entries, medical or barangay records, photographs of injuries, threatening messages and call logs, the names of witnesses, and the identity of the person who threatened you. Note the date the threat ended, because the action to annul must be brought within the period the law allows counted from the time the violence or intimidation ceased — not from the date of signing. In the meantime, do not perform under the contract or accept benefits from it, since that may be read as ratification. If you have been forced into a deed, a waiver or a loan, book a consultation before the period runs out.