We’re having a similar problem. It’s not the actual page that is indexed, it’s the download link. Google is indexing the PDF file.
http://www.domain.com/?wpdmact=process&did=xxxxx
We’ve added the below to robots.txt but they don’t work.
User-agent: Googlebot
Disallow: /*.pdf$
User-agent: *
Disallow: *.pdf # Block pdf files. Non-standard but works for major search engines.
Any suggestions?