Quote Originally Posted by Soft sign View Post
Не читав письмо от мамы, он ушёл. — he has read nothing in the letter
That's not really Russian no matter how you look at it. In modern Russian, at least, perfective adverbial participles (деепричастия совершенного вида) are only formed from perfective verbs. For "читать" the corresponding form is "читая".