I have read this lesson and i think that stating that the tense of the verb following has to be the past participle would clear the confusion.
Under the table showing how to conjugate these regular verbs in the present perfect it's saying "You can see it is simply haber conjugated in El Presente plus the Participio (ending in -ido)."
I have included a link that takes you to the explanation about past participles.
I hope that makes it clearer.
Gracias y saludos
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