Does reading a specific section of a book by an author with different religious leanings, while disregarding these leanings, fall under the Hadith (لا ضرر ولا ضرار - "There shall be no harm or reciprocating harm")? And is being convinced by his words in this regard considered disbelief (kufr) or a sin?

The Ahmadiyya is a deviant and disbelieving sect. The Salaf warned against sitting with people of innovation and listening to them, out of fear of corrupting hearts and spreading doubts. The heart is weak, and doubts are captivating. It is forbidden to look into the books of people of innovation except for one deeply rooted in the Qur’an and Sunnah, with great steadfastness, strength in religion, excellent discernment, and sharp intelligence, for the purpose of refuting them, exposing their secrets, and tearing down their veils. Therefore, it is obligatory to avoid looking into the books of this man and other misguided individuals, and to suffice with the books of the people of Sunnah. And Allah knows best.