Enumerate all extensions from registry with their host application

uses Registry;

procedure TForm1.Button1Click(Sender: TObject);
var
  reg: TRegistry;
  keys: TStringList;
  i: Integer;
  typename, displayname, server: string;
begin
  memo1.Clear;
  reg := TRegistry.Create;
  try
    reg.rootkey := HKEY_CLASSES_ROOT;
    if reg.OpenKey('', False) then
    begin
      keys := TStringList.Create;
      try
        reg.GetKeyNames(keys);
        reg.CloseKey;
        {memo1.lines.addstrings(keys);}
        for i := 0 to keys.Count - 1 do
        begin
          if keys[i][1] = '.' then
          begin
            {this is an extension, get its typename}
            if reg.OpenKey(keys[i], False) then
            begin
              typename := reg.ReadString('');
              reg.CloseKey;
              if typename <> '' then
              begin
                if reg.OpenKey(typename, False) then
                begin
                  displayname := reg.ReadString('');
                  reg.CloseKey;
                end;
                if reg.OpenKey(typename + '\shell\open\command', False) then
                begin
                  server := reg.ReadString('');
                  memo1.Lines.Add(Format('Extension: "%s", Typename: "%s", Displayname:"%s"' +
                                         #13#10'  Server: %s',
                                         [keys[i], typename, displayname, server]));
                  reg.CloseKey;
                end;
              end;
            end;
          end;
        end;
      finally
        keys.Free;
      end;
    end;
  finally
    reg.Free
  end;
end;