I don't believe any auto-magic commands just do this kind of calculation, it's much too complex of a question for a typical BB function to solve. I'm actually not even entirely sure what you're really trying to do, as it's not like every piece of rebar will be drawn in BB or on plan, or anywhere else, unless you got a really bored drafter or cluttered drafting standards.
You can layout an area calc in BB and give it a thickness for volume purposes, but you can easily do that outside of BB once you have the area, too. For any kind of linear take off, you're just going to need to trace over the info you are trying to take-down with the length measurement and convert each measured length to the corresponding rebar type and length, etc.
Maybe I'm missing some awesome functionality that BB has, or that any pdf viewer could even have, but I don't think so.
