Not exactly. The .msk files allow you to have not transparent white areas in your .bmp files.

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>It does the same thing as the one I can accomplish with editing the .bmp file directly. Is it safe to say that it isn't a necessary file anymore?
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>>The .msk files can be used to control transparency of a .bmp. It's covered in VFP9 help under How to: Enhance Control Display.
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>>>I always see corresponding .msk files for most .bmp files in the VFP folders. How are the .msk files used?
>>>
>>>I usually just edit the .bmp files in Paint and set the Opaque property off then fill the background with a White color and save the same .bmp file. This makes the .bmp transparent in the VFP controls.