function ExtractTemporaryFiles(const Pattern: String): Integer;

Extracts the files matching the wildcard specified by Pattern from the [Files] section to a temporary directory. Returns the number of extracted files. To find the location of the temporary directory, use ExpandConstant('{tmp}').

The extracted files are automatically deleted when Setup exits.

An exception will be raised if no files were extracted successfully, no files were found, or if files were found but none could be processed because of their MinVersion and/or OnlyBelowVersion parameters.

Use Flags: dontcopy in the [Files] section to tell Setup to skip the file during the normal file copying stage.

When solid compression is enabled, be sure to list your temporary files at (or near) the top of the [Files] section. In order to extract an arbitrary file in a solid-compressed installation, Setup must first decompress all prior files (to a temporary buffer in memory). This can result in a substantial delay if a number of other files are listed above the specified file in the [Files] section.

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

[Code]
function InitializeSetup: Boolean;
var
  S: AnsiString;
  ResultCode: Integer;
begin
  // Show the contents of Readme.txt (non Unicode) in a message box
  ExtractTemporaryFiles('{tmp}\Readme.txt');
  if LoadStringFromFile(ExpandConstant('{tmp}\Readme.txt'), S) then
  begin
    MsgBox(S, mbInformation, MB_OK);
  end;

  // Extract all MyProg files and launch it. Note how {app} is left unexpanded.
  ExtractTemporaryFiles('{app}\MyProg.*');
  ExecAsOriginalUser(ExpandConstant('{tmp}\')+'{app}\MyProg.exe', '', '',
    SW_SHOWNORMAL, ewWaitUntilTerminated, ResultCode);

  Result := True;
end;

ExtractTemporaryFile