This might be the cause. If so, there's a fix of sorts to keep the crashes from happening:
For More Information see: Records with a PDF file linked to an active container field cause FMP 12 to crash in OS 10.9
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