Man pages matching name libpbm in section 3:

libpbm.3.en	debian 10 / libnetpbm10-dev
libpbm.3.en	debian 10 / libnetpbm9-dev
libpbm.3.en	debian 11 / libnetpbm10-dev
libpbm.3.en	debian 11 / libnetpbm9-dev