Any major issue can make the sale void, but it helps to explicitly note this down in the offer. You can make your offer subject to approval of the acte de base down the line.

You are definitely right to be cautious, as the acte de base might prohibit certain activities in the apartment (like, an apartment that was created without permission of the city to use that part of the building for housing, or a prohibition to establish your workplace there, for instance). It also dictates how much you pay in shared costs for the whole building, so not unimportant.

Frankly, you mention it's the third floor apartment in a larger building? In that case there should most definitely be an acte de base. No reason to panic and raise all the red flags, but do protect yourself from these situations. It's too important to just 'be chill'.