Is it possible to get pregnant while using a placebo?

I started taking Atywia Daily, but one thing puzzles me. Does it protect "all the time"? Namely, in the leaflet I read that taken from the first day of the cycle protects immediately against pregnancy, from 2-5 you should use additional protection for a week, but the placebo period is not explained there. If I take all 21 white tablets properly, is there a possibility of pregnancy with a 7-day hormone withdrawal? When I take them correctly, am I protected at all times, regardless of the blister tablet number? I happen to have sex during menstruation, hence my doubts.