Level and brace the door frame first so the foam cannot bow it while expanding. Above freezing, moisten the surfaces and do not fill the gap to the top: the foam keeps growing. MAX DUO 2-in-1 applied with a gun barely post-expands, so fill the joint to 2/3.

For fire doors choose B1 fire-rated foam. Trim the cured foam and protect it from UV with a casing, paint or plaster.