Hi I just gutted my bathroom and switched the location of the toilet bowl. I cut into the 4'' cast iron stack used a adapter and now its running a 3'' abs about 5 feet from the stack.so what I would like to know is if I must vent the toilet bowl because it is 5 feet away now and also if I can use a 90'' elbow to connect my toilet bowl [using a flange of course]

so what I would like to know is if I must vent the toilet bowl because it is 5 feet away now and also if I can use a 90'' elbow to connect my toilet bowl
Unless your local codes mandate a separate vent for each fixture your toilet bowl will wet vent through the lavatory vent. If you're asking if you can use a quarter bend and raiser in place of a closet bend, the answer's yes you can. Good luck. Tom