NDFan is correct. Conversion from a paper ticket to an e-ticket requires, among other things, that the agent go through the laborious process of (a) deciphering the tax and fee codes, then (b) manually re-entering them into the relevant fields on the screens for the e-ticket. This must be done for all 20 segments, regardless of how many flights have been flown already. When I had this done last year, the conversation between the ATO, RTW desk and the tariff office (all 3) took over an hour, and ultimately required that some portions of the taxes/fees lines be "collapsed" into shorthand since the form fields on the screens didn't have enough space to accommodate the whole magilla.

If you do this at a small station (mine was at SEA) be prepared for the process to take more than a day, because they may not have the staffing to dedicate one person (usually a supervisor) to go through all this cr@p while trying to deal with customers at the counter.

To be honest, unless you need to do a re-issue, I'd just keep the paper tickets and save yourself (and save some poor AA employees) the serious hassle.