You sure can. But, remember, barns are typically not made to last the test of time, like winterized homes are and their structures may not be constructed to hold the weight of conventional home building necessities. It is certainly doable, with the right amount of cash. Renovations often cost more or as much as a new build, so be wise to do your research before beginning such an extensive project.
I love the house-barn look and the possibilities of a unique interior build with lofts and open areas that a barn structure offers. You know, you can also get a barn style post and beam home built from scratch.
Adapting an old bar into a residence will take an engineer with plans to convince your local building and zoning officials that the structure will be sound and comply with all regulations. But, it can and has been successfully done. Good luck to you.