Final Draft 7 is not supported on OS X 10.12 (Sierra), 10.11 (El Capitan), 10.10 (Yosemite), 10.9 (Mavericks), 10.8 (Mountain Lion) or 10.7 (Lion).
While OS X allows for longer file names, earlier Mac operating systems don't. Because Final Draft 7 and 6 run in the earlier operating systems as well as OS X, the program conforms to those systems for the length of the file name, which is why it won't allow you to extend the file name. If you change the file name outside the program, it won't recognize the long string of characters and will shorten it this way.
Note: Final Draft 10 / 9 / 8 support long filenames. Information on the upgrade to Final Draft 10 is HERE.
NOTE: Live support for Final Draft 7 has been discontinued. You will still be able to install, activate and use FD7 on appropriate computers but email, chat and telephone support is no longer available. Live activation assistance will be available via phone (818-789-6281) and email and chat (links on the left side of this page) until June 14, 2017.