using shims on milgard windows
 

i am installing milgard classic vinyl windows (nail fins).
to make sure that the window is level, i might have to add
shims before nailing the bottom fin.

can i place space shims between rough sill and the bottom of the
window? will using shims here cause the window to

sag? should the shims be placed only at the corners?

once the window is square and nailed in place, can i remove all the
shims? or should i just leave them alone or do i

need to nail the shims as well?

thank you in advance.

thank you.