いたす, or
致（いた）す as it is often written, is a 謙譲語（けんじょうご） (humble speech)
う-Verb, which refers to the actions of the speaker (or people within the speakers inner circle, like their company). Similarly to
お〜する,
いたす means ‘to do’.
In the case of
する verbs themselves, simply replace
する with
いたす. For other verbs, add
いたす to the ます stem of the verb, while attaching お, or ご to the beginning (depending on whether it is a word of Japanese or Chinese origin).
Words that include the kanji 拝（はい） ‘to worship’, or ‘to revere’, do not usually require お, ご, or
いたす. This is due to the word itself being ‘respectful’.
-
私（わたし）は親戚（しんせき）のお寺（てら）を拝観（はいけん）する。
I will look at my relatives' temple. (With utmost respect)
-
先輩（せんぱい）からお金（かね）を拝借（はいしゃく）する。
I will borrow money from my senpai. (With utmost respect)
いたす is considered to be slightly more humble than お〜する, which means that it will be heard more frequently in advertisements, or being used by company employees.