Roughly: “pol dee la vay-ree-tay.”
Three common ways:
No. In French you generally need a determiner with count/abstract nouns. Say Paul dit la vérité.
There is, however, the idiomatic alternative Paul dit vrai (“Paul is telling the truth”), where vrai functions adverbially.
Use the passé composé: Paul a dit la vérité.
Note that the past participle is also dit. For a habitual/ongoing past sense, use the imparfait: Paul disait la vérité (“he used to/was telling the truth”).
Use dire que + clause: Paul dit que c’est vrai. (“Paul says that it’s true.”)
Use dire à [personne] de + infinitive to report telling someone to do something: Paul dit à Marie de venir.