These two verbs often overlap, but with exceptions. I actually find it difficult to explain how to properly use each one, but let’s say that pensar relates more to the act itself of thinking, while achar refers to a specific opinion you hold. In sentences such as the one you posted, they may overlap:
O que acha o Pedro dos seus jornais?
O que pensa o Pedro dos/sobre os seus jornais?
In other cases, it’s easier to see what sets them apart:
Estou a pensar em ti. (I’m thinking about you)
Estou a achar em ti. (gibberish)
Achar may also mean to find. This seems more common in Brazilian Portuguese, but it’s also accepted in European Portuguese.
Having trouble distinguishing between these two verbs. Both translate to ‘to think’ but I can’t seem to discern when to use one over the other besides memorizing phrases.
Portuguese seems to have several of these pairs of verbs where there is a subtle difference that we don’t have in English. I think penchar / achar is a bit like olhar / ver or falar / dizer.
Pensar = the act of thinking or pondering about something, e.g. eu penso em religião
Achar = the outcome of that thinking process, so is more used for opinions, assumptions or beliefs, e.g. eu acho que Jesus é o filho de Deus