[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program
OutputDir=userdocs:Inno Setup Examples Output

[Files]
Source: "MyProg.exe"; DestDir: "{app}"; BeforeInstall: OnBeforeInstall
Source: "MyProg.chm"; DestDir: "{app}"; BeforeInstall: OnBeforeInstall
Source: "Readme.txt"; DestDir: "{app}"; Flags: isreadme; BeforeInstall: OnBeforeInstall

[Code]
procedure OnBeforeInstall;
var
  CurrentFile: string;
  CurrentFolder: string;
begin
  CurrentFile := ExpandConstant(CurrentFileName);
  CurrentFolder := ExtractFilePath(ExpandConstant(CurrentFileName));
  MsgBox('Folder: ' + CurrentFolder + #13#10 + 'File: ' + CurrentFile, mbInformation, MB_OK);
end;