FLDIGI Users Manual 4.0
The developers recommend that you build either fldigi from source or install from the repository associated with your distribution. The repository may not be immediately available for the most current version number. In that case you can try installing the binary distribution. Keep in mind that the version numbers of the dependent shared libraries must match those on the machine used to create the binary.
The source code for fldigi is very large and has a number of dependencies that must be satisfied before a successful compile. If you are not familiar with compiling and linking source code you should probably practice on a simpler package before treading these waters. Please refer to the following web site for information on building for Linux, Windows and OS X.