actually the armor is made of a metal called Ceramite and is one of the strongest metals in the Warhammer 40k universe and it can with stand acid of all types. so basically yeah it's acid proof. don't believe me here's the info.
Ceramite is a form of heat and shock-resistant ceramic material that is widely used throughout the Imperium of Man. High-quality ceramite is used in the higher-quality types of Imperial armour, including Carapace Armour, Power Armour and Terminator Armour. Ceramite conducts almost no heat, making it especially heat-resistant and effective protection against energy-based weapons. Low-quality ceramite is used to mass-produce cheap Flak Armour for the Imperial Guard. An inexpensive and sturdy building material widely used across the Imperium consists of pulp wood formed around a core of low-grade ceramite. This material is used for the construction of low-cost prefabricated housing blocks on many Imperial Hive Worlds.
and did you notice that it said heat-resistant yeah and that also means that lightsaber can't do jack shit to the armor.
would've been better in my opinion if the Space Marine had been using a chainsword, but Bolter or bolt pistol (hard to tell) works just as well. Just don't bring a Space Marine Terminatro into the mix. Or Jump Packs.