Why does boron trifluoride $(BF_3)$ behave as a Lewis acid?

(N/A) The electronic configuration of boron $(B)$ is $2s^2 2p^1$. It has three electrons in its valence shell.
Thus,it can form only three covalent bonds with fluorine atoms.
This means that there are only six electrons around the boron atom in $BF_3$,and its octet remains incomplete.
Because the boron atom is electron-deficient,it has a vacant $p$-orbital that can accept a lone pair of electrons.
Hence,$BF_3$ acts as a Lewis acid.