There is a max current rating, a max voltage rating, and a max junction temperature rating (or case rating).
You can't run it at max current and max voltage (from input to output) without getting a high power dissipation.
Low voltage and high current may be OK, as may high voltage and low current.
To dissipate lots of heat, you need a heat sink.
To calculate temperature (and compare it to the max temperature rating), you need to know the power dissipation (in W) from the voltage difference and load current and relevant thermal resistance (K/W) to the ambient temperature (which may rise above 25 C inside a box).
Then, you need to know the thermal resistance to ambient, which depends on your heat sink (that information can be hard to find--keep looking).
If the device is specified for case temperature, you only need the heat sink resistance (plus a bit for the interface or a bit more for a mica washer, if you use it) in K/W.
If the device is specified for junction temperature, it should specify the internal thermal resistance (K/W) from junction to case.