Guillaume,
The .lfp format is an extension to the .fp format that is used by NI-supplied libraries, (such as all the CVI libraries that show up in your library menu when you start up CVI. You can see the files in the CVI\bin folder). Roughly speaking, it stands for "Library function panels". The only two differences between an .lfp and an .fp are:
1. An .lfp is not editable in the Function Tree Editor.
2. An .lfp takes advantage of linked help. In a typical large library, many functions and parameters share the same help content. By allowing these to be linked from a master copy of the help, it reduces the overall size of the file greatly.
There is no difference in their relationship to the corresponding program module (.c, .obj, .lib).
Luis