Hello,
PDF24-creator is not Windows Installer based. This is the reason why the application is not listed in the drop-down.
Only MSI files have an UpgradeCode (part of Windows Installer technology). An EXE does not and cannot have an Upgrade Code unless it installs or unpacks an MSI internally.
Since you can’t obtain an Upgrade Code here, you’ll need a different detection method. Two common alternatives are:
1. File version check. For example, test that "C:\Program Files\PDF24\pdf24.exe" exists and matches desired version.
2. Registry check. Look for a key such as: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\{…}
and verify the DisplayName/DisplayVersion values.

- registry version.png (70.16 KiB) Viewed 1219 times
Hope this helps! Let us know if you have any questions.
Best regards,
Liviu