This article provides more detail on RA's technology, and helps me pinpoint my unease:
"Every time the PDF is read, it briefly interacts with the reporting repository to record the event."
It's one thing to track a file transfer, and quite another to monitor reading habits. Apparently, I'm not alone - Forrester Research has also cautioned RA that end users may react quite negatively to "what they perceive as intrusiveness if they perceive that they do not benefit on their end."
What he said.