Adding filename extensions to files (FileMaker Pro Advanced)
You can use the Developer Utilities to give non-runtime FileMaker database files the FileMaker file extension. This is useful for cross-platform development, if you want the filename extension to be consistent on both Windows and Macintosh platforms.
To add the FileMaker filename extension to non-runtime databases:
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Choose Tools menu > Developer Utilities.
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Click Add to locate the files that you want to customize.
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Select Databases must have a FileMaker file extension, and click OK.
Related topics 
Binding files into a runtime solution (FileMaker Pro Advanced)
About creating runtime solutions (FileMaker Pro Advanced)
Displaying databases in Kiosk mode (FileMaker Pro Advanced)
Removing Admin access to databases (FileMaker Pro Advanced)
Saving solution settings (FileMaker Pro Advanced)