Are the conductors inside the cable rated as THHN? If they are could I remove the cable casing to use the wires in a buried conduit?

Southwire® Romex ® Brand SIMpull® NM-B (nonmetallic-sheathed) cable may be used for both exposed and concealed work in normally dry locations at temperatures not to exceed 90°C (with ampacity limited to that for 60°C conductors) as specified in the National Electrical Code. NM-B cable is primarily used in residential wiring as branch circuits for outlets, switches, and other loads. NM-B cable may be run in air voids of masonry block or tile walls where such walls are not wet or damp locations. Voltage rating for NM-B cable is 600 volts. https://www.southwire.com/wire-cable/building-wire/romex-brand-simpull-type-nm-b-cable/p/63950002 To see the construction of THHN, go to: https://www.southwire.com/wire-cable/building-wire/simpull-thhn-wire-with-alumaflex-brand-conductors/p/BW15