A Himalayan bear entered a BSNLoffice in Gangtok on Wednesday and attacked a sub-divisional engineer, injuring him on his face and head, police said.Forty two-year-old Arvind Yadav was resting in one of the rooms of the BSNL office in Sadar police station area when the bear attacked him, an officer said.Yadav sustained injuries on his face and head and was admitted to a hospital, he said.Forest officials later reached the spot and tranquillised the bear, the officer added.