That's an emphasized form of も as the objective marker. Incidentally, もが also works as the subject marker in the same usage, for instance, 誰もが知っている, 彼女までもが賛成した.
e.g.
ヒトのどんな組織をもつくることができるとされる細胞を取り出すことに成功したのだ。
このような可能性をも考慮しつつ、まずはイラクの戦後復興に、
仕事も自分の内面をも限定された安定的なものに変えていくことが考えられる。
その反対側をもあわせると六四相にものぼります。
国家主権をもこれまでよりは強く発揮することに賛成し、支援をしている。
何とかでき得る限りの助成措置をも勘案しながら、
Well. That's a bit of a shock. I would have sworn I was taught that you can *never* have をも and must *always* replace を with も.
So perhaps I misunderstood, and that lesson was only supposed to apply to the "also"/inclusive use of も, and not the "even"/emphatic use,
but even then, you have:
をも can be used also for "too/also", but it has a nuance of "even" as a result since it's emphasized. So, その本 has a nuance that it's usually not read, for instance, too difficult to read, uninteresting/valueless to read or like that in その本をも読んだ。.