If you look at other threads you will see some debate on the use of the present perfect, so expect some of the great people here to disagree with me. - especially as you have picked an example where, in my view, both tenses can be understood to mean exactly the same thing!Originally Posted by Hanka
"I co-founded" in your example sentence says to me that you did this at some time in the past. The company may still exist today, but what you are concentrating on is a single finished action in the past. You co-founded it, you managed it, you sold it........
"I have co-founded" in your example could also refer to a single finished action, but could also be referring to something which started in the past but which has a connection to the present.
A lot depends on what time or other expressions you use:-
I co-founded.......in 2001/when I was younger.
I have co-founded.........since 2001.