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While the National Electrical Code does not expressly forbid inserting NM cable inside conduit, in practice, it is very difficult to do so, and very few professional electricians will do such an installation. THHN wires are relatively inexpensive and are much easier to run through conduit.
Keeping this in consideration, is it OK to run Romex in conduit?
one reason you don't put romex in conduit is because it creates more heat and is not advised in conduit if you have conduit you can run insulated wires instead it's probably cheaper. when you put romex inside conduit The Romex cannot breathe and retains too much heat.
Also to know is, what type of wire can be run in conduit?
The most common type of cable used in home wiring is non-metallic (NM), or Romex, cable. While NM cable can be run inside conduit, this is seldom done. The types of wire most commonly installed inside of conduit are THHN and THWN. THHN/THWN wires are individual, insulated, and color-coded wires.
Re: Exposed romex NM cable is permitted to be run exposed on the surface of the building finish. If subject to physical damage then it requires supplemental protection. The term subject to physical damage is not defined by the NEC so it becomes an interpretative issue.