Hello,
sorry for the late reply. Since version 11.11.0, PDF24 Creator requires at least Windows 10, and the installer checks this when it starts. Windows Server 2012 R2 is based on Windows 8.1 and is therefore no longer supported; the current version cannot be installed there. 11.10.2 was the last version that could be installed on it.
Please use PDF24 on a newer Windows version. Without installation, the PDF tools are also available online in any browser: https://tools.pdf24.org/en/