Private Declare Function DeleteFile Lib "kernel32" Alias "DeleteFileA" (ByVal lpFileName As String) As Long
Private Declare Function FindExecutable Lib "shell32.dll" Alias "FindExecutableA" (ByVal lpFile As String, ByVal lpDirectory As String, ByVal lpResult As String) As Long
Private Declare Function GetTempPath Lib "kernel32" Alias "GetTempPathA" (ByVal nBufferLength As Long, ByVal lpBuffer As String) As Long
Function GetExePathFileFromExtention(ByVal  sExtension As  String) As  String
    Dim sPath As String, lRet As Long, sBuffer As String, FF As Integer
    
'   on récupère le chemin TEMP
    sBuffer = String$(512, vbNullChar)
    lRet = GetTempPath(512, sBuffer)
    sPath = Left$(sBuffer, lRet)
    If Not (RightB$(sPath, 2) = "\") Then sPath = sPath & "\"
'   on crée un fichier  temporaire
    sPath = sPath & Format$(Now, "MMDDHHNNSS") & "." & sExtension
    FF = FreeFile
    Open sPath For Output As #FF
        Print #FF, vbNullString
    Close #FF
'   on récupère l'exe associé
    sBuffer = String$(260, vbNullChar)
    lRet = FindExecutable(sPath, vbNullString,  sBuffer)
'   retour
    If lRet > 32 Then
        GetExePathFileFromExtention = Left$(sBuffer, InStr(sBuffer, vbNullChar) -  1)
    Else
        GetExePathFileFromExtention = vbNullString
    End If
    
'   supprime fichier  temp
    Call DeleteFile(sPath)
End Function

[DllImport("kernel32.dll")] 
static extern uint GetTempPath(uint nBufferLength, [Out] StringBuilder lpBuffer);[
DllImport("shell32.dll", EntryPoint="FindExecutable")]
static extern long FindExecutableA(string lpFile, string lpDirectory, [Out] StringBuilder lpResult); 
public static string GetExePathFileFromExtention(string extension) 
{

    string tempFileName = Path.ChangeExtension(Path.GetTempFileName(), extension);
    string tempPathFile = Path.Combine("temp", tempFileName); 
    StringBuilder sb = new StringBuilder(1024);
    File.Create(tempFileName); 
    long ret = FindExecutableA(tempFileName, string.Empty, sb);
    if (ret >= 32) return sb.ToString(); 
    else return string.Empty; 
}

function GetExePathFileFromExtention(const aExt: String): String;  
var sTmpPath, sTmpName: String; 
    iLen: Integer; 
begin 
  SetLength(Result, MAX_PATH);  
  SetLength(sTmpPath, MAX_PATH); 
  iLen := GetTempPath(MAX_PATH,  PChar(sTmpPath)); 
  SetLength(sTmpPath, iLen); 
  sTmpName := sTmpPath +  FormatDateTime('MMDDHHNNSS', Now); 
  if aExt[1] = '.' then 
    sTmpName  := sTmpName + aExt 
  else 
    sTmpName  := sTmpName + '.' + aExt; 
  with TFileStream.Create(sTmpName, fmCreate or fmShareDenyWrite) do  
  try 
    iLen := FindExecutable(PChar(sTmpName), nil, PChar(Result)); 
  finally 
     Free; 
    DeleteFile(sTmpName);  
    if iLen < 32 then 
       Result  := EmptyStr; 
  end; 
end; 
{Utilisation} 
procedure  Tfrm_Main.Button1Click(Sender: TObject); 
begin 
  Label1.Caption :=  GetExePathFileFromExtention('Txt'); 
end;