Both .fp5 and .fmp12 files seems to be databases from various versions of FileMaker Pro software. It is not clear whenever these two files may actually be converted between each other, or from what version they originate, but it is likely they can be only handled by FileMaker and no other 3rd party software.
Convert FileMaker Pro database file to FileMaker Pro database file.
We have found 2 software records in our database eligible for .fp5 to .fmp12 file format conversion.
Microsoft Windows software - convert fp5 to fmp12 on Windows
A program used to create and manage information databases
Convert from fp5 file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned fp5 to fmp12. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert fp5 to fmp12 on OS X
A database management program for Mac