What is the Preceding Direct Object (PDO) rule?

It's easy to worry about rules with complicated names like this one, but they're normally simpler than they sound. This rule only applies with 'passé composé' and pluperfect phrases. When the direct object (or direct object pronoun) comes BEFORE the verb, you need to remember to make the past participle AGREE with the object. E.g. Marie? Je l'ai vue hier / Les devoirs que j'avais faits... / Les bières que j'ai bues ce soir...