办公司=办+公司--------set up a company 办公室=办公+室--------office

办公室 is a noun,means office。 “办”in “办公司”is a verb，means "set up",创办。 there are some meaning of “办”： ◎处理：办公，办事，办理。 ◎处分：惩办，法办。 ◎置备：办置，办货。 ◎创设：创办，兴（xīng ）办。

'办/公司' means 'to set up/start a firm/company'. It's a phrase, verb[V]+Noun/Objetive[N/O]. '办公·室' means 'an office'. A room, set of rooms or building where people work, usually sitting at desks.

办公司，means start a firm/company. it's a verb phrase. 办公室, the office, it's a noun.