Short answer. Yes. Rule 8, Section 6 of the Rules of Court requires that an authenticated copy of the judgment or decision be attached to the pleading when you plead a domestic or foreign court's judgment. So an authenticated copy of the foreign judgment must accompany your complaint.
What the law says
In pleading a judgment or decision of a domestic or foreign court, judicial or quasi-judicial tribunal, or of a board or officer, it is sufficient to aver the judgment or decision without setting forth matter showing jurisdiction to render it.
Rule 8, Section 6 — Judgment. Read the full provision →
What the law says
An authenticated copy of the judgment or decision shall be attached to the pleading.
Rule 8, Section 6 — Judgment. Read the full provision →
Yes, an authenticated copy has to be attached
Rule 8, Section 6 states the requirement directly: an authenticated copy of the judgment or decision shall be attached to the pleading. Because you are suing based on a foreign court's judgment, that judgment falls squarely within what this section addresses, and the copy attached to your complaint has to be authenticated, not simply a plain or uncertified reproduction of the ruling.
What the section spares you from having to plead
The same section also simplifies what you have to allege about the judgment itself: in pleading a judgment or decision of a domestic or foreign court, judicial or quasi-judicial tribunal, or of a board or officer, it is sufficient to aver the judgment or decision without setting forth matter showing jurisdiction to render it. You do not need to plead out the facts establishing that the foreign court had jurisdiction; averring the judgment itself is enough on that point.
Domestic and foreign judgments are covered by the same sentence
Section 6 does not set up separate rules for local and foreign judgments; both are addressed in the same breath, alongside decisions of quasi-judicial tribunals, boards, and officers. That means the attachment requirement, and the simplified pleading rule about jurisdiction, apply to your foreign judgment exactly as they would apply to a judgment issued by a Philippine court, without any extra layer of pleading.
What this means for your complaint
Since you are suing on a foreign court's judgment, Section 6 requires you to attach an authenticated copy of that judgment to your complaint. What it does not require is a separate showing, within the pleading itself, of the facts that gave the foreign court jurisdiction to issue it; averring the judgment is enough for that part of your complaint to stand.
Why the article does not spell out how authentication is done
Section 6 tells you that the copy must be authenticated, but it does not itself describe the mechanics of authenticating a foreign judgment. That detail sits elsewhere in the rules governing how foreign public and official documents are proven. What this section fixes is the pleading requirement: attach an authenticated copy, and you need not separately plead the foreign court's jurisdiction.