That's a known issue with FileMaker 12.
For More Information see: PDF prints as an image
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: https://www.dropbox.com/s/jt09b82i0xijbu3/FMP%20Bugs.zip
Thanks so much for your reply. Think we'll need to pull some custom reports for a while!