Question

how should knockdown door frames be stored?
flat and against a concrete floor or surface
flat and off the floor
upright, in the position they will be installed
horizontally with spacers between the doors

Explanation:

Knockdown door frames should be stored flat and off the floor to prevent warping and damage. Storing them flat helps maintain their shape, and keeping them off the floor protects them from moisture and dirt that could be present on the floor.

Answer:

flat and off the floor