#define AppName "Version1"

[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program

[Files]
#if AppName == "Version1"
  Source: "Version 1 File.txt"; DestDir: "{app}"
#elif AppName == "Version2"
  Source: "Version 2 File.txt"; DestDir: "{app}"
#else
  # error Unknown AppName define value
#endif