An auxiliary/conjunction attached to the imperfective form meaning 'even if not doing' or 'without doing.' It's somewhat formal or emphatic and often used in writing.
見ずともわかるだろう。
You can probably understand it even without seeing it.
助けを借りずとも自分でやってみるつもりだ。
I intend to try doing it myself even without help.
お金がなくとも幸せに暮らせる人もいる。
There are people who can live happily even without money.