You can, though sometimes it's easier to cut out the old trap and install a new trap at the same time.
I am replacing the bath tub in my older house and found a cast iron p trap. The old drain was brass. Can I connect a PVC drain to the cast iron P-trap?
If YOU can make a connection to it, then go ahead.
Licensed residential and commercial plumber
Thanks for the input. I did a bit more research and found it to be brass p trap and drain that I had removed. I am going to put a PVC drain in and see what happens.