Does window film prevent a break-in? Is it bulletproof?

Yes, window film may help break-in. While an accident happens, the window film holds the glass securely in the window frame, which offers two advantages. First, to prevent the glass from shattering, window film reduces the risk of falling glass. Also, It decreases the risk of walking on broken glass shards. Secondly, even when the window is shattered, the glass can act as a barrier from rain and wind.
Window film can't protect your building from bullets; if you are looking for protection against guns, the bulletproof glass may be the one you are looking for.