Thanks for posting.
You're correct, FileMaker 12 can only directly convert files in the .fp7 format. For this issue, the .fp5 files will need to be converted to .fp7 first. Do you have access to a .fp7 application (FileMaker Pro 7-11) to convert to? If not, let me know and I'll see what I can do to help out.
For reference, here is a link to our Knowledge Base article listing the conversion path for all versions.
Well .. rats. Thought I had a version 7 around here somewhere, but unfortunately no.
No worries. The best option is to contact FileMaker Customer Support at 1 800-325-2747 to help you convert your file to .fp7. I have also sent this information in a private message. You can check this by clicking on the Inbox link in the upper right corner of this forum.