Hydraulic fittings are designed so that no dope is needed. The metal to metal contact does it all. But sometimes stuff goes wrong in the field, and so there is such a thing as hydraulic pipe dope.
You can use hydraulic dope but there are some rules.
First of all is to get the special type for high pressure hydraulics - NOT the type you use for water and gas service and other general plumbing. The hydraulic kind stands up to hot oil and stays plastic long enough for the pressure to force it into the gaps to be sealed....but soon stiff enough not to get pushed on through.
Next is that you generally only want to put it on the male threads and not on the first couple of those. The idea being to make sure that any excess dope is forced out of the joint as it is assembled. That also means that you shouldn't loosen and re-tighten the joint. Yeah, I know that it's hard to get the hydraulic fittings lined up right the first time. We all cheat a little on this one..... That's why we didn't put dope on the first couple of threads.
So you want to think twice before using it on any fitting that you may need to take apart in the future. Most hydraulic pipe dope is designed for permanent fittings. Sometimes taking it apart is necessary but involves careful disassembly followed by lots of cleaning of the threads (I use dental tools) to prevent chunks of dope from getting into the hydraulic circuit where it can wreck the close tolerance pumps and valves. The ones that advertise as making the joint reusable don't mention that they are depending on your having thought about the relationship of your hydraulic filtration to the flow path.....here's hoping they aren't being too optomistic.... Anyway, it's not a good plan to use the stuff on any fitting that you plan to take apart regularly.
But all of that is not to say that the pipe dope doesn't have its place. It does. Just think it through & keep your brain in gear.
rScotty